A cohort of 101 male carbaryl production workers with at least 1 yr experience in the carbaryl area was selected from employment records. Of these individuals, 47 provided satifactory semen samples for analysis; 36 of the 47 provided blood for hormone assay. There were no major age or employment-status differences between those who agreed to participate and those who did not. In the absence of sufficiently detailed industrial hygiene exposure data, a subjective exposure classification was developed. No apparent relationships were found between sperm count and exposure category or years worked in classifications based on carbaryl exposure. Also, no relationship was found between fathering children and exposure to carbaryl. When the sperm-count distribution of the carbaryl-exposed workers was compared with a distribution of sperm counts representing a nonexposed (control) population, no overall differences were observed that could be related to carbaryl exposure. There was a small excess in the number of sperm counts less than 20 million per milliliter among the carbaryl-exposed men, but the excess was not significant at alpha = 0.05.