The response to a rapid intravenous administration of adrenocorticotropin (ACTH, cortrosyn) was compared in 24 unexplained infertile women and 13 fertile women. There was no significant difference in the response to a rapid ACTH stimulation as expressed by the slope of testosterone (T) response in both groups. However, the individual and mean T values prior and following the stimulation were significantly higher in the infertile group (P less than 0.001; P less than 0.005, respectively). There was no significant difference in individual values as well as in mean basal values or in mean values of 17-hydroxyprogesterone (17-OHP) after the stimulation between the two study groups (P less than 0.3; P less than 0.9, respectively). There was no significant difference in individual values as well as in mean values of dehydroepiadnrosterone (DHEA) before or 90 min after the stimulation between the two study groups (P less than 0.1; P less than 0.2, respectively). It can therefore be concluded that the elevated basal testosterone values in the infertile group originated from the ovary. Despite the fact that no attempt was made to reduce androgen values 7 (46.66%) of 15 infertile women who were available for follow-up and treatment conceived following ovulation induction therapy.