Reviewing previous studies of patients with various sex-hormone anomalies and from his own experience, the author concludes that: 1. Estrogens are specific for female and androgens for male secondary sex characteristics irrespective of genetic or gonadal sex. 2. The level of libido or sex drive (the author equates the two) is hormonally influenced and androgen is probably the libido hormone in both men and women. 3. The male and female sex hormones have a direct male and female effect making them erotically functional. 4. The direction or content of the sex drive is not determined by the sex hormones.