From ken some interesting news from a New York Times article:

By the time they arrive in Beijing, most athletes have resigned themselves to the possibility of undergoing a battery of tests for banned substances, like anabolic steroids and certain cough medicines.

But some male athletes may find they are asked to submit to an entirely different examination — one that will test whether they are, in fact, men.

Organizers of the Beijing Olympics have set up a sex-determination laboratory to evaluate “suspect” male athletes, the official Chinese news agency Xinhua reported Sunday.

*note: the above citation was slightly altered to underscore a point.