OBJECTIVE This study focused on determining the testicular function of greenhouse workers exposed to pesticides. METHODS Semen was examined for 122 of 199 eligible men (61%) from 30 ornamental flower greenhouses. Sperm concentration, morphology, and viability were measured according to World Health Organization guidelines, and the curvilinear sperm velocity was determined by a computer-assisted analysis of video recordings. Three groups were formed according to expert judgment of current exposure to pesticides from cultures, pesticide formulations, and the transfer of pesticide residues from leaves to hands, and also ranked according to years of work in a greenhouse. The risk estimates were adjusted for the effects of sexual abstinence and other potentially confounding factors. RESULTS According to current exposure the median values of sperm concentration and the proportion of normal spermatozoa were 60% and 14% lower, respectively, in the high-level exposure group (N=13) than in the low-level group (N=44), and the values of the intermediate group fell in between. The adjusted differences between the high-level and low-level exposure groups were statistically significant, while no differences were observed for the viability and velocity of sperm and sexual hormones. The median sperm concentration was 40% lower for the men with > 10 years' experience in a greenhouse than for those with < 5 years' experience. The age-adjusted testosterone/sex-hormone-binding globulin ratio declined 1.9% (95% confidence interval 0.4-3.4%) per year of work. CONCLUSIONS The results are compatible with the hypothesis that male fecundity may be at risk from exposure to pesticides in the manual handling of cultures in greenhouses.