The adverse effects of organophosphate dimethoate on testis histology and luteinizing hormone (LH) cells in the adenohypophysis of the Nile tilapia (Oreochromis niloticus) were examined. Adult male tilapias, average body weight 150±23.3 gm, were exposed to sublethal dose (5.00 mg/L-1) and environmentally relevant dose (0.03 mg/L-1) of dimethoate for 15 and 30 days. Exposed male tilapia to Dimethoate at 5.00 mg/L-1 for 15 and 30 days exhibited significant (P