The gonadal steroids--estrogens and androgens--appear to have a mood-elevating, psychotonic effect. The improved sense of well-being and increased vigor probably is engendered by restoration of somatic efficiency and psychic equilibrium. 1. The male climacteric, as observed in a limited number of men, is associated with a low level of serum testosterone. The levels of follicle-stimulating hormone and luteinizing hormone are not elevated because estrogen concentration continues unaltered well into old age. Androgen replacement therapy often lessens fatigue, depression and headaches, and headaches, and improves libidinous drives. 2. In the aging female, many climatric symptoms other than those due to vasomotor instability were heretofore considered merely coincidental. Recent studies suggest that the metabolism of cerebral hormones is markedly influenced by endogenous and exogenous gonadal steroids. Thus, postmenopausal depression, headaches, and nervousness may be hormone-dependent symptoms. 3. The incidence of endometrial cancer is no greater and is probably less in estrogen-treated women than in women not treated with estrogen, if regular cyclic courses of an oral progestogen are added to the regimen.