The Improv Olympic West invites you to join the weekly antics of a Broadway-style musical made up on the spot, based on audience suggestions.
From the IO West website:
Every night is the `Opening Night' of a musical that has never been seen! Now in it's fourteenth year, Opening Night: The Improvised Musical! is thrilled to continue the show LAWeekly called, "almost too slick to be completely improvised."
Click the above link for more information.