Evidence is presented for man that libido and potency may be normal despite a diminished supply or even complete absence of gonadal substances. Although end-organ sensitivity is directly affected by hormones, the libidinous urge is largely psychologic and is little influenced by them. In homosexuality, there is no observed correlation between a choice of sex object and level of hormone secretion. Sex hormones do not seem to be important in determining "sexual mannerisms" and attitudes. It is emphasized that any valid approach to human sexuality must deal with the total individual. The genetic, the hormonal and the psychologic factors must all be taken into consideration. In general, the genetic factor lays down the particular type of sexual pattern, the hormonal substances bring about the growth and increase the sensitivity of the sexual organs, the psychologic or learned factor may greatly increase or repress sexual activity irrespective of endocrine status. Psychologic deviations are chiefly responsible for abnormalities in human sexual behavior. Endocrine imbalances play at most a secondary role.