John Belushi, Bill Murray, Gilda Radner in never-broadcast footage

Sunday night, NBC television will celebrate the 40th anniversary of the hit comedy show Saturday Night Live with a three-hour celebration of the sketch and satire program's colourful and coloured history.

SNL, performed before a live audience since 1975, has spoofed politicians, lampooned popular culture and broadcast fake commercials so convincing that viewers sometimes were unaware that the products advertised weren't real. The program also highlighted top music stars with two performance segments in each episode.

In its long run, SNL brought breakout exposure for dozens of comedians whose stars continue to shine in sitcoms and on film.

Many of the initial performers on the program got their start in the Second City comedy clubs, and on the edgy, risqué-for-its time National Lampoon Radio Hour.

In the 1970s, CBC Television went behind the scenes at the Radio Hour to meet this new breed of comedian. The documentary that this footage was shot for was never completed or aired. But portions of partially edited segments remain.

In it, you'll see future stars — John Belushi, Bill Murray, Gilda Radner, Harold Ramis and others — before they rose to international stardom as the pioneers and icons of SNL and Second City Television.