Declining male fertility and environmental factors.

Male reproductive function has recently attracted increasing attention due to reports on time-related decline in semen quality. Analysis of retrospective data indicates that sperm counts may have declined in some parts of the world, but there seem to be regional differences both in the quality of semen and regarding the secular trend. Whereas data on sperm counts may be somewhat difficult to interpret, there is no doubt that incidence of testicular cancer has increased worldwide. In occupational studies, only a few types of exposures were shown to have an impact on male reproductive function; lifestyle and general environmental factors may play a more important role. Prospective studies on secular and geographic trends in male reproductive function are warranted.