I never saw it, but it starred a young woman named Sydne Rome, with whom I had gone to Carnegie Tech (now Carnegie-Mellon).

As I remember from glancing through the novelization at the time, it turns out in the end that the film called WHAT? is about a film called WHAT? Very meta...

Sydne must have become resident in Europe, because she also played Louise Bryant in an Italian film about her and John Reed (played by Franco Nero) that came out around the same time as REDS, which starred Diane Keaton and Warren Beatty.