The effects of pesticide contamination of drinking water on human reproductive health are largely unknown. In a statewide survey of 856 Iowa municipal drinking water supplies in 1986-1987, a rural water system supplied by the Rathbun Reservoir was found to have elevated levels of the herbicide atrazine, 2.2 mcg/l vs. 0.6 mcg/l in other Iowa surface water supplies. Rates of low birth weights, prematurity, and intrauterine growth retardation (IUGR) in live singleton births during 1984-1990 in women living in 13 communities served by the Rathbun water system were compared to other Iowa communities. The Rathbun communities had a significantly greater risk of IUGR than southern Iowa communities with other surface sources of drinking water. Multiple linear regression analyses revealed that levels of the herbicides atrazine, metolachlor, and cyanazine were each significant predictors of community IUGR rates in southern Iowa after controlling for several potentially confounding factors including maternal smoking and socioeconomic variables. The association with IUGR was strongest for atrazine, but all three herbicides were correlated. The independent contributions of each to IUGR risk could not be determined.