I read a journal article recently, that discussed measuring testosterone levels in a colony of Rhesus monkeys. They found that lower-status males had lower testosterone levels than the dominant males, which stands to reason. However, the interesting part of this was that if the dominant male was removed, and another took his place, that new monkey would have his own testosterone levels rise as a result. This implies that monkey and human males' testosterone levels can potentially be affected *by our own perception of our status within a group*. (There was also the possibility that dominant males had more sex than the other males, and that affected testosterone levels, but I believe they controlled for this somehow. I don't have access to the journal right now to look it up.)
Then I realized that my own perception of my social status seemed to strongly correlate with my desire to cross-dress throughout my life. Or rather, I felt more female, the less control I felt I had over my own life. Granted, that's just me, but I'm curious to see if others here might feel the same way.
The other thing that leads me to suspect testosterone could play a role, is that most cross-dressers tend to dress up the least, during periods of their lives that are associated with high testosterone levels, and vice versa. That is, it's common before puberty, less common after, and is often the least frequent during college years, (around 18-25) when testosterone levels are particularly high. Then, cross-dressing seems to become more common after 30 or so, as testosterone levels drop. The same is true of sex drive as well. We already know that sex hormones can have significant effects on our behavior, and this could be another instance of that.
I'm not 100% sure that I'm right about this, but I think there could be something to it. Theoretically, a cross-dresser who wished he didn't want to cross-dress, might have a particularly low testosterone level, and a doctor could prescribe something that would raise it.
But of course, those of us who are just fine the way we are can always just keep doing what we're doing.