The relative semen quality of workers not exposed to toxicants were examined in a longitudinal study and compared with six control groups with known toxicant exposure. In the longitudinal study, 45 Ohio men, ages 25 to 35 years, provided monthly semen samples for 9 months. Comparison control groups consisted of 19 pesticide workers in Colorado (CO), 44 pesticide workers in Hawaii (HA), 37 foundry workers in Oregon (OR), 41 ship painters in Connecticut (CT), 34 dielectric sealer operators in Maryland, and 31 soldiers in Texas (TX). Sperm viability, sperm count, and sperm motility were determined. The mean sperm count for all samples was 47.43 million sperm per milliliter. The studies in CO, HA, OR, and CT had higher sperm counts than the longitudinal study. Mean semen volume was 2.78 milliliters, which did not differ among groups. The average sperm count per ejaculation was lower for the longitudinal study than for all control groups. Sperm hypoosmotic swelling and pH did not differ significantly from the longitudinal study. Sperm morphology differed from the longitudinal study for all but CO and TX. The authors conclude that the longitudinal study of unexposed Ohio men is useful for calculating power/sample size and serves as a benchmark for new controls. The comparison of other control groups to the Ohio group reinforces its quality and usefulness in such analyses.