Elevated prostate cancer incidence was found at a plant producing atrazine that had an intensive prostate screening program. This study tested the relationship among atrazine exposure, prostate cancer, and the screening program. Twelve cases and 130 control subjects were selected from the original cohort. Prostate screening and occupational histories were abstracted from company records and atrazine exposures were estimated. Hire date was comparable for cases and control subjects. Nearly half of the control subjects and no cases left before the prostate-specific antigen (PSA) screening program. Cases had more PSA tests than control subjects (odds ratio for ≥1 test, 8.54; 95% confidence interval, 1.69-82.20). There was no association between atrazine exposure and prostate cancer when those with ≥1 test were compared. There was no evidence for an association between atrazine and prostate cancer.