I really enjoy a soak in a hot tub, especially late at night and before sleep. I used to do this almost every night. As a doc, I alwasys knew that men who expose themselves to elevated temperatures could suffer reduced fertility, but was unaware of any studies that confirmed the effect of frequent hot tub use. Well, it appears that the study is in. As reported in the NY Times, researchers at UC San Francisco measured decreased fertility in men who soaked daily in hot tubs... The good news was that after 3 - 6 months of abstinence (from hot tubbing), the sperm counts improved about 5-fold!
There is a new release on the study here http://pub.ucsf.edu/newsservices/releases/200702283/
Here is the NYT piece: "THE BOTTOM LINE Regular exposure to hot tubs can hurt male fertility, though the effects can be reversed"