The purpose of this experiment was to investigate the effects of experimental cryptorchidism on the levels of testicular FSH, LH receptor. One hundred and thirty two male rats weighing 100${pm}$10g, 45 days old, were divided into three groups of control, bilateral cryptorchidism and unilateral cryptorchidism which was subdivided into two groups of scrotal testis and abdominal testis. Thirty to forty two heads of rats were allotted to each group. Five to eight rats from each group were randomely sacrificed at 1, 2, 3, 4 and 5 weeks after surgical induction of cryptorchidism. Testis was removed for assay of FSH, LH receptors. The results obtained were as follows. 1. The levels of FSH receptors per 10mg testicular tissue in abdominal testis of unilateral cryptorchid group and bilateral cryptorchid group tended to decrease gradually toward 5th week and these levels at 2nd, 3rd, 4th and 5th week were significantly lower than those levels of control group and scrotal testis of unilateral cryptorchid group. On the other hand; the ranges of affinities of FSH receptors of abdominal testis in unilateral and bilateral cryptorchid group were 2.2 - 6.67 ${ imes}10^{11}M^{-1}$ and 3.6 - 4.8 ${ imes}10^{11}M^{-1}$ respectively, and these values were slightly higher than those of control group (1.43 - 3.98 ${ imes}10^{11}M^{-1}$) or those of scrotal testis in unilateral cryptorchid group (1.41 - 3.25 ${ imes}10^{11}M^{-1}$). Especially at I and 4 weeks after treatment the affinities of abdominal testis in unilateral and bilateral cryptorchid group were significantly higher than those of other group (P <0.01). 2. The levels of LH receptors in 10mg testicular tissue tended to increase with elapse of time in control and in scrotal testis of unilateral cryptorchid group. But the levels of LH receptors of abdominal testis in unilateral and bilateral cryptorchid group tended to decrease after treatment and were significantly lower than control group at 1 (P <0.01),2,4 and 5 weeks after treatment (P < 0.05). The affinities of LH receptors were not significantly different among treatments except those of bilateral cryptorchid group and abdominal testis of unilateral cryptorchid group being significantly higher than that of the control at 4 weeks after treatment.