YOU'RE sitting in the cinema watching a Soppy Movie with subtitles about 17-year-old Spanish Estrellita, who is in love with a French medical student, Jean-Francois. It's been on a while. As you sink into this frantically kitsch tale, a man in the audience stands up and shouts abuse at the screen. Then a red-haired woman in a suit accuses her neighbour of trying to touch her up. Then some football hooligans heckle and honk horns. The ushers run up and down the aisle flashing torches.

Back on screen the love story has become a film within a film. We are watching a story about the people who make the soppy movie. The backstage events on the screen compete with the off-stage events in the cinema. A fight breaks out in the aisles. The characters in the movie are aware of the people in the cinema. They face out and ask them to shut up. The racket continues. The actors from the movie walk through the screen and on to the stage. They argue with members of the audience. Members of the audience walk on to the stage, through the screen and into the movie. They do. They really do. Woody Allen, eat your heart out.

Blinded by Love is an ingenious comedy about film and theatre. It premiered in Barcelona (as Cegada de Amor) in 1994 and has been a smash hit all round Spain. The most daringly successful fusion of film with theatre, it switches with breathtaking zaniness between at least four levels of reality. By the end, genuine members of the audience - as opposed to the "plants" who had disrupted the film earlier, join a fully costumed religious procession that takes place half on stage and half on screen.

The company La Cubana started out in the 1980s as an amateur group doing open-air performances, happenings, and mixing real people with fictional characters. The writer and director Jordi Milan takes on the whole subject of what-is-truth, what-is-reality with an anarchic zest that jumbles up Fifties advertising, soap opera, panto and Pirandello. The manic disruptiveness disguises enormous discipline. While the correlation between what the actors do on stage and what they do in the movie is so exact, you wonder what happens to this show when one of the cast gets a stomach bug.

You wouldn't expect a French director/designer making his English language debut with a Shakespeare to root his production so rigorously and insistently in the text. But that is what Stephane Braunschweig does with his new Measure for Measure. A projection of Masaccio's Adam and Eve Banished from Paradise appears on the set: the characters engaged in the play's fiercely argued moral debates come across with the poise and dignity of figures in frescoes.

Braunschweig's Vienna is a grim, imprisoning world of metal staircases and semi- circular black walls that slide round (pushed with sisyphean patience by the cast) to a cacophonous industrial soundtrack. Except for these ominous scene changes, the actors are in charge. When Isabella, played with determinedly cool earnestness by Lise Stephenson, pleads with the watchful, thin-lipped Angelo (excellent Paul Brennen) for the life of her brother, they follow the shifts in the argument with the precision of chess masters. We feel they know the full weight of what they are saying. The sobriety is - in its own way - intoxicating. Later, when Stephenson threatens to expose him, Brennen stands high up on the staircase, his eyes and half his face in shadow, and asks with the cool levelness of a marksman: "But who will believe you?" Braunschweig's spare and uncluttered accuracy gives each side its full measure.

'Blinded by Love': Int'l Conference Ctr (0131 473 2000) to 23 Aug; 'Measure for Measure': Royal Lyceum (0131 473 2000) to 26 Aug.