Objective To observe the effects of estradiol benzoate (E_2),human cberionic gonadotropin (hCG) and luteinizing hormone-releasing hormone (LHRH) on testicular descent and their relation to the expression of insulin-like factor-3 (INSL3) mBNA in rats.Methods At birth,40 SD male rats were assigned to 4 groups,and each group consisted of 10 rats.Each group received injection of one of the following drugs:normal saline(NS),E_3,hCG+E_2,and LHRH+E_2 for 29 clays after birth.Total RNA was extracted from the testis on day 30 after birth.INSL3 was synthesized and further amplified by RT-PCR.Results (1) Testicular descent rate on clay 30 after birth was 100% (20/20) in the group of NS,0% (0/20) in the group of E_2,85% (17/20) of hCG + E_2,and 70% (14/20) of LHBH + E_2.There was no significant difference between the last two groups ( P = 0.45).(2) Weight of testis differed significantly among the groups ( F = 56.67,P＜0.01 ),being lightest in the group of E_2.(3) E_2 could damage the germ cells of testis,however hCG and LHRH ameliorated this situation. (4) The expression of INSL3 mBNA was absent in the group of E_2,while the other groups showed normal expression.Conclusion E_2 inhibits testicular descent in rats,while hCG and LHRH promote the progress.The mechanism seems to be related to the expression of INSL3 mRNA.