Sidemen were the foot soldiers of popular music in a time long past. They played in the Big Bands of the Swing era, in the orchestra pits of musical comedies, at weddings and parties, as the backing for recording artists and in cabaret and jazz concerts. For most of those who heard their music, they must have been like the wallpaper behind the singers and band leaders who fronted them. But, though they weren't stars, many of them were musicians of the highest quality. The best of them had the technique and artistry to hit the highest heights, but hadn't had the luck or the personality or whatever it is that raises a performer above his peers. Only their fellow-musicians, or that small coterie that would maybe get to hear them jamming among themselves in some late night joint, would know just how good they were. Though they were for hire for virtually any musical function that would have them, at heart, first, last and all the time they were jazzmen. Meanwhile they went where the work was, no matter how low grade. As a character in Sideman says, on his way to a bad club date: "I play as well as they let me".

Leight's Tony Award-winning stage work is autobiographical. His father was a trumpeter for over 50 years and, in the play, the ups and downs (mainly downs) of his career are narrated by his son.

the good times, being a sideman was no bed of roses. The hours were murder, the pay indifferent and there could be long periods out of work. The sidemen were constantly changing bands, going on lengthy and exhausting tours and falling out with their employers over money. The incessant travel around America inevitably made family life almost impossible. What made it at all bearable, of course, was the music, the joy of playing that obsessed them to the exclusion of virtually everything else.

The play catches the sidemen at a turning point in their profession, the 1960s and the advent of Elvis Presley rock 'n' roll. Within a few years the whole nature of popular music changed and with it also jazz, which has always used the great standard tunes of the 1930s, 1940s and 1950s as a starting point from which to build its improvisations.

The big bands, since their inception, had always been crucial in popularising Broadway music, but now they were out of date. Whether you believe pop was dumbed down or that it was replaced with something more visceral and of the people, the undoubted fact was that music became less sophisticated.

The guitar, an instrument that, unless it was played at the highest level, required less skill than the traditional instruments of the orchestra, became the chief icon of the new music. Home-made groups produced home-made songs for themselves and brought them into the recording studios, where to this day they often have to be beefed up with the help of more skilled session musicians, the sideman's modern heirs.

MOST of these musicians hated the new music with its insistent beat, its lack of swing and melody and its general crudity and lack of lyricism. Probably it was partly jealousy at the greater success of the new form. Partly it was dismay over the dilution of a great tradition, and partly it was just a matter of taste - some people hate what others love.

But whatever way you looked at it, it marked the end of the sidemen. As Clifford, the play's narrator, says: "These guys are not even a endangered species any more. It's too late. There are no more big bands. No more nontets, or tentets. No more 60 weeks a year on the road. No more jam sessions till dawn in the Cincinnati Zoo. When they go, that'll be it."

Like all good plays, Sideman has resonances beyond its immediate subject. Its obsessive hero, who neglects his child and drives his wife to alcoholism, could be any workaholic. As someone says: "He was usually at work, but even when he was home, he wasn't home", which could apply to many an accountant, businessman or whatever.

But it also captures the way musicians talk and think, and how funny they can so often be, too, so that its faded sub-culture of club dates and bus tours, of drink and other drugs, of tough language and sweet music, seems a real loss.

Sideman, of course, has music in it, but it's very much in the background, so that we never really hear its characters playing. There is a beautiful moment when, at the end of the night, a group of musicians sits around and plays a bootlegged tape of the great trumpeter Clifford Brown playing Night in Tunisia on the evening before he was killed in a car crash. As they sit listening to the wonderful music you can understand what it is that they hope and dream and their dusty lives take on new meaning.

Sideman runs from Tuesday, July 18th to Saturday, July 22nd at the Black Box Theatre at 8 p.m.; there are matinee performances at 2.30 p.m. on Wednesday, Friday and Saturday