Twelve black patients with primary amenorrhoea as a result of hypogonadotrophic hypogonadism were studied to establish the diagnosis of isolated gonadotrophin-releasing hormone (GnRH) deficiency. All were eunuchoid with poor development of breasts and pubic hair. Chromosomal complement was female and none had midline facial defects or anosmia. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels were low or undetectable, while the levels of other pituitary hormones were normal. Patients did not respond to clomiphene citrate administration, but did bleed in response to an oestrogen/progestagen combination and responded to human menopausal gonadotrophin. This study clearly establishes that isolated GnRH deficiency occurs in black women and suggests that the male:female ratio is different from that in white populations.