The plasma LH, FSH and testosterone response to LRH was studied in 12 boys with compensatory testicular hypertrophy (CTH) and normal puberty and in a matched control group with normal testicular development. It was found, that the boys with CTH had normal basal plasma testosterone and LH concentrations; at the same time the basal plasma FSH level were significantly higher than in the control group. The response of plasma LH and FSH to LRH was markedly greater in the CTH group than it was in the control group. It is concluded, that the contralateral testicular hypertrophy which enables a normal pubertal process is the result of increased secretion of gonadotropins, mainly FSH.