Five years ago, to celebrate his 70th birthday, Pierre Boulez presented a major retrospective of his own music with the London Symphony Orchestra. Now Boulez 2000 will mark his 75th birthday (which falls in March) with concerts in 11 cities around the world.

The programmes concentrate on the 20th-century scores he has championed throughout his career, alongside the premieres of specially commissioned orchestral works from Olga Neuwirth, George Benjamin, Peter Eotvos and Salvatore Sciarrino.

The first programme on Thursday set a standard the rest of the series will do wonderfully well to match. There is no composer that Boulez conducts better than Alban Berg, and there is no conductor who more completely understands Berg's unique combination of emotional power constrained by structural rigour or who realises it in performance with more shattering effect. It is impossible to imagine a more masterly or definitive performance of the Three Orchestral Pieces than the one Boulez unleashed here, with the LSO encouraged to produce playing of immense sinewy intensity and faultless virtuosity, with every layer of this teeming score utterly lucid and every climax faultlessly judged.

It was balanced by Mahler's Sixth Symphony at the opposite end of the programme. When conducting Mahler, Boulez is sometimes a little ruthless, pushing through lyrical passages (like the swooning second subject of the Sixth's opening movement, or the main theme of its Andante) without giving them quite enough room to breathe; but his ability to clarify texture is more than adequate compensation. The last movement is the most elaborately structured of all Mahler's finales and the hardest to bring off, but Boulez got it exactly right.

Between those towering Viennese masterpieces Olga Neuwirth's Clinamen/Nodus was never going to stand much of a chance, but as the first major score by this 31-year-old Austrian to be heard in Britain it would have been a disappointment in any circumstances - the wild, swirling textures, scored for a huge orchestra with copious percussion, are laced with Varèse-style sirens and the kind of "meta-music" effects made fashionable in the 80s.

•At the Barbican on February 2 and 27, and March 2. Box office: 0171-638 8891