Three black women, daughters of the same father but three unrelated mothers, presented with isolated gonadotropin deficiency (IGD). Clinically, the patients had no midline defects and intact smell and taste senses. Biochemically, the essential feature was very low unstimulated and stimulated follicle-stimulating hormone and luteinizing hormone levels, even after priming with gonadotropin-releasing hormone over a 5-day period. Growth hormone response to insulin-induced hypoglycemia was somewhat blunted, but prolactin, cortisol, and thyroid-stimulating hormone responses were quite normal. All three patients had the 46,XX karyotype; clinical or biochemical aberrations could not be demonstrated in any of the remaining family members. The disorder was, apparently, transmitted by the deceased father, who manifestly did not have an IGD deficiency nor any of the midline stigmata associated with IGD. The mode of inheritance seems most likely to be autosomal dominant with variable penetrance.