The Birthday Party by Harold Pinter, directed by Adrian Mulraney. With Chris Brown, Jo Buckley, Bruce Kerr, Adrian Mulraney, Nicki Paul and Stephen Whittaker. St Kilda Army & Navy Club Memorial Hall, 88 Acland Street, St Kilda, until May 27. Bookings 0431 739 211

Fourplay by Jane Bodie, directed by David Ryding. Design by Emma Caporn, audio design and music by Craig Tracy, lighting design by Aaron Beach. With Brett Whittingham, Olivia Hogan, Kate Gregory and Dan Walls. Actomatic @ Cromwell Rd Theatre, 27A Cromwell Rd, South Yarra, until May 26. Bookings 9429 8118.

The Birthday Party's notorious debut has no doubt warmed the cockles of many a disconsolate playwright's heart. One of the earliest plays by the then little known playwright Harold Pinter, it opened in the West End in 1958 to total disaster. The critics slaughtered it and its total takings, when it closed after a week, were a dismal £260 11s 8d.

But enter the hero (for once, a critic). Harold Hobson of The Sunday Times showed his mettle by disagreeing vocally with his colleagues. "I am willing to risk whatever reputation I have as a judge of plays," wrote this good gentleman, "by saying... that Mr Pinter, on the evidence of this work, possesses the most original, disturbing and arresting talent in theatrical London".

This is not a fairytale, so the play didn't return at once to rapturous audiences; but posterity has shown that Hobson's instinct was remarkably acute. The Birthday Party is among the most famous post-war British plays, and Hobson's review marked the first major recognition of Pinter's talent, which has now lifted him to the status of cultural monument. This is not necessarily, it must be said, an unambiguous good, and Pinter has never sat cosily in the armchair of the Great British Playwright, as the controversy around his Nobel Prize amply demonstrated. But that's another story.

Seeing The Birthday Party almost 50 years later, it's easy to understand why Hobson was so convinced of Pinter's unique, unsettling gift. For all that has changed since the '50s, the play remains as radical and mysterious as it must have been on its first outing. The comfortable truisms about "human nature" that Pinter so ruthlessly attacked in that play are, I suspect, as present now as they were then: they may have changed costumes, but their certainties and judgements lie as heavy as ever.

One of the perils of being a cultural monument is the settling of dust. Pinter is often paid obesience here, if rather uneasily - I remember, on the occasion of his 60th birthday, that the Age asked a number of local playwrights what his influence was on their work. They mostly jumped like startled hares, made bad jokes about pauses, and strenuously denied any influence at all - which an unkind person might have observed was abundantly evident in their plays. His recent plays, among the most exciting of his career, are assiduously avoided by our major companies, and the only chance I've had recently to see his plays on stage is in co-op productions. Which can be a mixed blessing indeed.

So kudos to this company of actors for putting on a compelling production of The Birthday Party. Directed by Adrian Mulraney, this production demonstrates the truth of the old saw that theatre is two planks and a passion. There's not a lot of money here: the design consists mainly of sheets pegged to the wall, and it's done three-quarters in the round (this may change with the exigencies of the new space: I saw the last night of its first season). Such "poor theatre" exposes two things, the text and the actor, and shows how little - and how much - it takes to make engrossing theatre.

The Birthday Party is set in a seedy boarding house - or at least, its hostess calls it a boarding house - supposedly run by Meg (Nicki Paul) and Petey (Bruce Kerr). There is only one boarder, Stanley, who seems to have an incestuously filial relationship to Meg, and claims to have been a pianist. Three figures arrive in this claustrophobic environment: Lulu (Jo Buckley), a young woman with unsuccessful designs on Stanley, and two sinister gentlemen, Goldberg (Stephen Whittaker) and McCann (Adrian Mulraney). It soon becomes clear that the two men are hunting Stanley, although it is never clear why. Meanwhile, Meg is planning to celebrate Stanley's birthday with a party, although he denies several times that it is in fact his birthday.

It's a play in which a great deal of the building anxiety depends on the inscrutability of the action: but despite the mysteries of the characters - we never know who Goldberg and McCann are, for instance, or why they are pursuing Stanley with such malevolent intent - it moves with a deeply unsettling verisimilitude. Mulraney and his fellow actors wisely eschew any imposition of "meaning" or interpretation upon a text which even the author refuses to eludicate. However, they do not conclude from this that Pinter is therefore merely "confusing", and that a confusing production will do to communicate the "confusions" of the text. Instead, these actors explore what director Carey Perloff has called the "frighteningly specific realism" that marks this work.

Pinter understands, as well as any writer ever has, how silence exists as much in speaking as in not speaking, and how language can be both a mask and a weapon. "Pinter's world," says Perloff, "is a predator's world...a world in which confession is fatal, in which the revelation of emotional truth leads to annihilation." In The Birthday Party, an unnerving sense of anxiety builds through the play, at different points exploding into obscurely motivated acts of violence: an attempted strangling, the beating of a drum.

At no point does Pinter release the tension by bringing a revelatory clarity to the action. What is given clarity, with the precision of a poet or a jeweller, are the specific details of human action and language. This production, notable for its excellent ensemble performances, is particularly effective because the actors pay this precision proper respect, giving the play a sinisterly heightened realism; the emphasis falls not on the "meaning" of the play, but its sharp, subtle, frightening dynamics. Instead, the play's meaning, in all its unsettling complexity, resonates deep inside the audience, in the unlit hollows of nightmare.

Another bunch of motivated actors is bringing Jane Bodie's Fourplay to the stage in South Yarra. Act-O-Matic is one of the impressive independent companies working in Melbourne: their production of Moises Kaufman's The Laramie Project was plain classy, justly winning them a Green Room Award, and they also do a line in plays by young expatriate Australian writers, producing Van Badham in 2004 and now Jane Bodie.

Fourplay concerns Alice (Olivia Hogan) and Tom (Brett Whittington), a couple in a long term relationship. Alice is a former actor, now turned social worker; Tom is rehearsing a play with the dangerously attractive Natasha (Kate Gregory). Meanwhile, at work Alice begins to make friends with her socially inept and perhaps slightly suspect co-worker Jack (Dan Walls).

This is the kind of scenario that generally has me gasping and clawing for breath by interval. But Bodie's writing shows why naturalism isn't always a recipe for television: she imbues her work with a subtly worked, intelligent theatricality, and her deliberately banal stories are leavened by a quick, sardonic wit. Perhaps most crucially, she has a gift for delineating the fractures that open between human beings; like a somewhat gentler Pinter, she understands how speech conceals as much as it reveals. Without a skerrick of sentimentality (except a rather too neat touch in the finale), she exposes the essential loneliness that lives, like a shameful, unacknowledged wound, inside human beings.

The set, featuring backlit abstract windows, is scattered with dead leaves, echoing the autumnal tone of the play. The actors perform the play well and honestly, realising the difficulty and pain that lies beneath the nervous skin of the script. They are hampered a little by David Ryding's direction, which lacks the fluidity of the writing: exits and entrances between the scenes simply take too long, and give the play a repetitive rhythm that doesn't serve it well. But overall it's a rewarding production of a fine play, and well worth the price of a ticket.