Olfactory perception thresholds and nasal mucous membrane function were measured over prolonged periods in 3 hypogonadal females; in 1 of these subjects nitrogen and sodium balance were also studied. Observations were made during periods of estrogen therapy (equilin sulfate, Premarin, estradiol-17[alpha],3-monosulfate), of androgen therapy (tesosterone propionate and nortestosterone), and of placebo administration. Estrogenic and androgenic effects were ascertained by measuring urinary gonadotropin and 17-ketosteroid excretions, respectively. Olfactory acuity during periods of placebo administration was not significantly different from acuity measured over long periods in 6 healthy women with normal gonadal function, but in the hypogonadal group there was a tendency toward pallor and swelling of the nasal membranes. Olfactory acuity increased significantly in 2 hypogonadal subjects while they were receiving estrogens, but this was not associated with significant changes in nasal function; throughout the study, their olfactory threshold values and corresponding urinary gonadotropin levels were correlated positively. In contrast, olfactory acuity decreased significantly in the third hypogonadal subject while she was receiving androgens, and there was a positive correlation between acuity and 17-ketosteroid excretion. During androgen therapy, this subject showed a modest increase in nasal swelling and secretions which might have contributed to the observed decrease in olfactory acuity. There was a positive correlation between nitrogen excretion and olfactory acuity, but there was no such correlation between sodium excretion and acuity. The mechanisms by which estrogens improve and androgens depress olfactory acuity in hypogonadal women remain obscure. However, there is a suggestion that local changes in the nasal membranes may contribute to these differences.