Scientific and public concern about the potential risk of environmental chemicals to male reproductive health has been heightened by reports of downward trends in semen quality, as well as increased rates of developmental urogenital tract anomalies and testicular cancer. Of particular concern is whether some contemporary-use environmental chemicals alter semen quality. Specific toxicants of interest include phthalates and pesticides, as well as polychlorinated biphenyls (PCBs). The human data on the relationship of semen quality with phthalate and pesticide exposure are limited and do not currently allow for a definitive conclusion on whether adult exposure, at background environmental levels, alters semen quality. However, the epidemiologic data support an inverse association of PCBs with reduced semen quality, specifically reduced sperm motility. The associations found were generally consistent across studies despite a range of PCB levels. In addition to the chemicals discussed, there are additional classes of chemicals that require further study on their relation with human semen quality.