This study aims at clarifying the semen indices of insecticide sprayers who are exposed mainly to organophosphorus and pyrethroid insecticides. Eighteen male sprayers out of 54 working for 9 companies in central Japan and 18 age-matched students or medical doctors as unexposed controls participated in detailed reproductive check-ups conducted in summer and the following winter. The sprayers were exposed to insecticides more in summer, the busiest season, than winter, the off-season (p<0.05). Erythrocyte true cholinesterase activities in the sprayers were lower than in the controls in summer (p<0.05), and decreased in significant association with the increase in exposure frequency. Testicular volumes in the sprayers tended to be smaller than in the controls (p=0.06). The serum testosterone concentration in winter in the sprayers was higher than in the controls (p<0.05), though luteinizing hormone and follicle stimulating hormone concentrations were not significantly different. The sperm counts and vitality were comparable between the groups, but detailed sperm motility analysis in summer revealed that the percentages of slow progressive and nonprogressive motile sperm were twice as high in the sprayers (p<0.05), and that of rapid progressive sperm tended to be lower (p=0.06). Such differences were not observed in winter. Differential sperm morphology counts showed that interaction of group and abstinence effects were significant in sperm with normal morphology and with head deformity only in the summer check-up. Despite possible inherent differences between the groups, the above season-dependent differences suggested that the observed lower semen quality in the sprayers was associated with pesticide spraying work.