In a previous study, compensatory dysfunction of the Leydig cell was identified in men in whom spermatogenesis had failed to recover after gossypol treatment. In this study, LHRH- (100 micrograms i.v.) and hCG (3000 IU i.m.)-stimulation tests were conducted in four controls and in 45 men who had used crude cotton seed oil as their cooking oil. The patients were divided into two groups: group A--17 men with normospermia or oligospermia and group B--28 men who were azoospermic. The basal serum LH and FSH concentrations were within the normal range in group A, whereas those in group B were increased markedly. There was no significant difference in testosterone levels between the two groups, although the levels were significantly lower than in the controls. The response of LH and FSH to LHRH, and of testosterone to hCG stimulation, were within the normal range in group A, whereas in group B the response to the LHRH test was increased significantly while their response to the hCG test was reduced markedly. It was concluded that the functions of the pituitary and Leydig cells remained unchanged in group A after long-term use of crude cotton seed oil, and that once azoospermia has occurred, it is followed by total testicular failure as indicated by the responses to LHRH and hCG tests.