Perhaps master director Billy Wilder, who knew how to make a sex comedy that actually had something substantial on its mind, could have made Sex and the Single Girl into a first-class romantic comedy. Unfortunately, director Richard Quine, though capable, is not Wilder, and Sex is not The Seven Year Itch or The Apartment; it's not even the equivalent of non-Wilder sex fare like Pillow Talk. What it is is a fairly standard-issue early '60s sex romp, long on complicated plot, short on simple logic. It also is a film that wants to have it both ways -- it wants to pretend that it's hip and sexy, but at heart it's square and rather smarmy. There is some clever dialogue, but there is also a fair share of one-liners that miss their mark. Don't blame the stars, who are all in good form. Tony Curtis knew how to play this kind of role in his sleep, and he brings his peculiar brand of charm to the part. Natalie Wood is appealing and amusing, and the two have great chemistry -- as do Henry Fonda and Lauren Bacall, although it's a chemistry of a totally different sort. Even Mel Ferrer does well, especially with his "martini dance." The cast manages to save Sex and the Single Girl, but neither they nor the overlong de rigeur climactic chase scene can make it a very good film.