Allegedly for their protection, women are relegated to jobs supposedly adapted to their unique physical capacities and excluded from jobs which are said to endanger their health. So-called women's jobs are claimed to reflect women's "natural" qualifications in requiring less strength, more dexterity, less emotional stability, and in involving less risk for potential offspring. But it is impossible to demonstrate scientifically the existence of biological differences between women and men which suit either sex for particular jobs. Working conditions which are cited to justify the exclusion of women are also harmful to male workers. It is concluded that the myth that job allocation respects biological qualifications serves employers by justifying low salaries and boring tasks for women, at the same time as it rationalizes men's exposure to risky and frightening working conditions.