The levels of LH, FSH and testosterone of three adult groups consisting of normal subjects, unilateral and bilateral cryptorcids were compared before and after LH-RH loading. It was found that both groups of cryptorchid had comparatively high plasma base line levels for both LH and FSH, particularly high in the bilateral group; and both groups responded to LH-RH loading. This indicates that their hypothalamo-hypophyseal systems were probably functioning normally. The plasma base line levels of testosterone were higher in unilateral cryptorchids than in the control group, and lowest in the bilateral cryptorchid group. But the reaction of testosterone levels to LH-RH loading was generally poor in both groups of cryptorchids, suggesting that, in cryptorchid cases, unilateral and bilateral, the capacity of the testicle to secrete testosterone is generally depressed, freeing central suppression. This probably accounts for the high values of plasma lh and FSH observed in such patients.