Receptors for FSH as well as FSH-stimulated cAMP production were measured in gonadal tissue of human fetuses of 8-16 weeks gestation and of rhesus monkey fetuses in the last third of gestation. A single population of high affinity receptors (Ka, 1.5-4 X 10(9) M-1) for human FSH was detected in testicular tissue of both species. Specific FSH binding was absent in the human ovaries but present in the two monkey fetal ovaries studied. FSH (1 microgram/mL) did not stimulate cAMP production in slices of any of the gonads studied (human fetal testes and monkey fetal testes and ovaries) or in cultured human granulosaluteal cells used in a control experiment, but FSH increased cAMP 10-fold in immature (10-day-old) rat testes. We conclude that the primate fetal testis, both during the first half and at the end of gestation, may be responsive to FSH stimulation, although this response does not involve the acute elevation of cAMP. In contrast, the absence of FSH receptors in early and midterm human fetal ovaries and the presence of such binding in this tissue in the late gestation monkey indicate that the ovary becomes responsive to FSH stimulation during later stages of fetal development.