To evaluate the effect of the levels of IGF-I in the epididymis and the expression of IGF-I in the testis of adult male rat after the administration of cyclophosphamide. Ninety-six male adult rats (8 weeks age) were divided into 6 groups. The doses given to the rats of the groups 1 to 5 were 10, 20, 40, 80 and 100 mg/(kg x d), respectively. The remaining group was served as control. All those rats were sacrificed and IGF-I were quantitatively determined by ELISA techniques 2 and 4 weeks after the administration of the drug (by gastric fudge). Immunohistochemical SP technique was used to examine expression of IGF-I in rat testis. The levels of cell factors (IGF-I) in the epididymis of the rats were gradually reduced with the increasing time and dose after administration of the drug. In the mean time the expression of IGF-I in the tissues of the testis of those rats were also gradually reduced. In the time of oligozoospermia/azoospermia induced by the administration of cyclophosphamide, the expression levels of