William Masters and Virginia Johnson conducted an important program of research on the physiology of human sexual response. They found that two basic physiological processes occur during arousal and orgasm: vasocongestion and myotonia. They divide the sexual response cycle into four stages: excitement, plateau, orgasm, and resolution.

Their research indicates that there is no physiological distinction between clitoral and vaginal orgasms in women, which refutes an early idea of Freud's. They also provided convincing evidence of the existence of multiple orgasm in women.

Criticisms of Masters and Johnson's model are that (1) they ignored cognitive factors and (2) their selection of research participants may have led to a self-fulfilling prophecy in their results.

Two cognitive-physiological models are Kaplan's three-component (desire, vasocongestion, and muscular contraction) model, and Walen and Roth's model, which emphasizes cognitive aspects of sexual response (perception and evaluation).

The nervous system and sex hormones are important in sexual response. The nervous system functions in sexual response by a combination of spinal reflexes (best documented for erection and ejaculation) and brain influences (particularly of the limbic system). There is evidence that some women ejaculate. Hormones are important to sexual behavior, both in their influences on prenatal development (organizing effects) and in their stimulating influence on adult sexual behavior (activating effects). Testosterone seems to be crucial for maintaining sexual desire in both men and women.

Pheromones are biochemicals secreted outside the body that play an important role in sexual communication and attraction. Much of the evidence is based on research with animals, but evidence in humans is accumulating rapidly.