Occupationally related, chemically induced sperm count suppression is a recently recognized problem, 1st discovered in connection with the manufacture and formulation of dibromochloropropane (DBCP). Sperm count data from 4 occupational cohorts, 2 exposed to DBCP and 2 exposed to epichlorohydrin (ECH), were studied. In both DBCP cohorts there was a significantly difference (.alpha. = 0.05) between sperm count distribution functions of the exposed group and of the non-exposed group. A much higher percentage of exposed men was oligospermic; the median sperm count for each exposed group was substantially lower than that for the respective non-exposed group. In the ECH cohorts there was no significant difference between sperm count data for the exposed group and for the non-exposed group. Exposure to DBCP, but not to ECH, was positively associated with detectable sperm count suppression. The key to identifying and assessing occupationally related sperm count suppression may lie in the proper classification and interpretation of group sperm count data.