Aim: To find out the toxic effect of endosulfan on the testicular function of pubertal rats. Methods: Male rats of pu-bertal age were orally administered endosulfan at a dose of 1.0 mg/kg body weight for 30 days. Twenty-four hours af-ter the last treatment, the rats were sacrificed and the testis, epididymis, seminal vesicles and ventral prostate were re-moved and weighed. A 10 % testicular homogenate was prepared for biochemical estimations. Results: In endosul-fan-treated rats, there were a reduction in the body weight and the weights of testis and accessory sex organs, a de-crease in the testicular lactate and pyruvate activities, and in the testicular DNA and RNA concentrations, whereas thetesticular protein concentration was slightly increased; the specific activity of testicular steroidogenic enzyme, 3β-OH-steroid dehydrogenase and the ascorbic acid level were decreased, which were correlated with a decrease in steroidoge-nesis. The lysosomal enzyme acid phosphatase and brash-border enzyme alkali Aim: To find out the toxic effect of endosulfan on the testicular function of pubertal rats. Methods: Male rats of pu-bertal age were orally administered endosulfan at a dose of 1.0 mg / kg body weight for 30 days. Twenty-four hours af -ter the last treatment, the rats were sacrificed and the testis, epididymis, seminal vesicles and ventral prostate were re-moved and weighed. A 10% testicular homogenate was prepared for biochemical estimations. Results: In endosul-fan-treated rats, there were a reduction in the body weight and the weights of testis and accessory sex organs, a de-crease in the testicular lactate and pyruvate activities, and in the testicular DNA and RNA concentrations, while thetesticular protein concentration was slightly increased; the specific activity of testicular steroidogenic enzyme, 3β-OH-steroid dehydrogenase and the ascorbic acid level were decreased, which were correlated with a decrease in steroidogesis. The lysosomal enzyme acid phosphatase and brash-bo rder enzyme alkali