Carbendazim, a metabolite of benomyl which is widely used as a fungicide, has been found to cause testicular and epididymal damage in laboratory rats, mice and hamsters. No studies of the effects of this chemical on the reproductive organs of birds have been reported previously. This report is that of an investigation on the response of the testis of the Japanese quail to experimental administration of this chemical in sexually mature and active birds. A single dose (400 mg/kg body weight) of carbendazim was administered orally to 20 quails that were sacrificed thereafter at 5 h, 3, 8 and 13 days post-exposure, at five birds spatio-temporally. Five birds acted as control. Testis weights and seminiferous tubular diameter as well as epithelial height decreased significantly from 8 day post-exposure. Epithelial histology was remarkably disrupted, and cessation of spermatogenesis occurred at 13 day post-administration of the chemical. Degenerative changes were uniform in each testis, and not patchy or multi-focal, as previously reported in the rat. The observed histological changes in the testis, due to carbendazim, were capable of causing prolonged infertility in exposed birds.