Organophosphorus compounds are widely used in industry, agricul ture and for publ ic heal th purposes. They are among the toxic compounds employed for insect control. The purpose of this work was to study histological , histochemical , as wel l as immunohistochemical changes that might occur in the testes of male Wistar rats because of chronic dimethoate intoxication. Treating rats wi th dimethoate (20 mg/kg) body weight daily for 15 and 30 days caused a decrease in number of germ cells, irregulari ty in of seminiferous tubules, loss of sperms, degeneration of intersti tial cells and congestion of blood vessels. Moreover, reductions in total polysaccharides and in total proteins content were detected. Immunohistochemical results showed an increase in the expression of proapoptotic protein (Bax) and antiapoptotic protein (Bcl2).The resul ts of this study confirmed that dimethoate seriously deteriorates the testes resulting in a decrease in fertility.