Testicular FSH and hCG receptors were measured in patients with Sertoli-cell-only syndrome (SCOS), and the value of Bmax for each hormone was compared with the value in subjects with normal testes. FSH receptor was detectable in only four of 10 patients, and the mean value of Bmax in four of the 10 patients was clearly lower than that in normal testes (p less than 0.005). On the other hand, hCG receptors were detected in all of six tested patients, and the mean value of Bmax was lower, but not remarkably so, than that in the normal testes. The function of Sertoli cells was remarkably impaired in most men with SCOS, whereas the function of Leydig cells was relatively preserved.