This study hypothesized that the variance in semen quality between geographic locations may be related to recent exposure to environmental toxins, particularly agricultural chemicals. Prospective, multi-center studies have demonstrated geographical variations in semen quality. A recent study of semen quality in four US cities found male partners of pregnant women a rural center (MO) to have significantly lower sperm counts and motility than men recruited from urban centers (NY, MN and CA). A small study of men from this population residing in MO demonstrated an association between semen quality and levels of urinary pesticide metabolites, while men in MN had few detectable levels. The study proposed to examine the relationship between semen quality and urinary pesticide metabolites in partners of pregnant women receiving obstetrical care at University of Iowa Hospitals and Clinics.