Dance: Trisha Brown Company, Queen Elizabeth Hall, London

When the American choreographer Trisha Brown created Set and Reset in 1983, she knew she had hit on a winning formula. Thirteen years later, the piece looks as fresh as ever; a mellifluously thrumming dance of convergence and retraction for seven performers who seem happily and haphazardly thrown together. Set and Reset marked the culmination of Brown's so-called "unstable molecular structure" cycle of works and, indeed, its skimming, bouncing drift, peppered with gentle collisions, suggests the busy fluctuations of contained atomic particles. Although Robert Rauschenberg's design - a suspended cube flanked by two pyramid forms upon which a spliced catalogue of film and newsreel clips are projected - sometimes detracts from the dancers' casual but muscular shimmying, it allows for a mischievous array of unintentional parallels between image and dance. Laurie Anderson's score provides a more organic accompaniment, its repetitive riffs and looping snatches of text (mainly the line "long time no see") fusing persuasively with Brown's dance.

The choreographer's latest work, MO, made to Bach's Musical Offering, is a hugely ambitious undertaking. For 30 years, Brown has been making dances in which she eschewed music altogether or incorporated it as an independent element. MO marks her first attempt at dancing to music. The work reveals Brown's staggeringly analytical dance mind in a series of choreographic permutations which play with the entire structure of Bach's 13-part composition. The nine dancers in plain black or white leotards and chiffon cloaks resemble a group of disciples following the music's hieratic creed and giving spatial expression to its aural patterns. The fastidious organisation and dazzling speed of their movement rarely let up: in this sense, the dance is as much a challenge for the viewer as for the performer, constantly bombarding the eye with its visible synthesis of retrograde and inversion wherein jumps spring into the floor instead of out of it, and helter-skelter runs are pulled back into schematic walks.

If You Couldn't See Me, Brown's first solo for 15 years, is another collaboration with Rauschenberg: he supplied the music - an unimposing tonal blur; the costume - a white, low-backed dress; and, in part, the idea that Brown should face away from her audience. That we are denied the front of her body has prompted Brown to concentrate on the communicative possibilities of the back. And, as she flips and capers, Brown offers us a privileged glimpse into the exquisite privacy of her dance.

n At the Theatre Royal, Newcastle tonight (0191-232 2061); Blackpool Grand, 3 and 4 June (01253 28372)

SOPHIE CONSTANTI