Masters and Johnson met in 1957 when William Masters hired Virginia Johnson as a research assistant to undertake a comprehensive study of human sexuality. According to author
Thomas Maier, as part of their clinical research Masters and Johnson observed paid volunteers engaging in sexual activity while hooked to wires in their lab. Masters and Johnson married in 1971 but then later divorced on March 18, 1993, in the Circuit Court of
St. Louis County; they nonetheless continued to work together professionally. Previously, the study of human sexuality (
sexology) had been a largely neglected field of study due to the restrictive social conventions of the time, with prostitution as a notable exception.
Alfred Kinsey and colleagues at
Indiana University had previously published two volumes on sexual behavior in the human male and female (known as the
Kinsey Reports), in 1948 and 1953 respectively, both of which had been revolutionary and controversial in their time. Kinsey's work, however, had mainly investigated the frequency with which certain behaviors occurred in the population and was based on personal interviews, not on laboratory observation. In contrast, Masters and Johnson set about to study the structure,
psychology, and
physiology of sexual behavior through observing and measuring
masturbation and
sexual intercourse in the laboratory. Initially, participants used in their experiments were prostitutes. Masters and Johnson explained that they were a socially isolated group of people, they were knowledgeable about sex, and that they were willing to cooperate with the study. Of the 145 prostitutes who participated, only a select few were further evaluated for their genital anatomy and their physiological responses. In later studies, however, Masters and Johnson recruited 382 women and 312 men from the community. The vast majority of participants were white, had higher education levels, and most participants were married couples. As well as recording some of the first physiological data from the human body and
sex organs during sexual excitation, they also framed their findings and conclusions in language that espoused sex as a healthy and natural activity that could be enjoyed as a source of pleasure and intimacy. The era in which their research was conducted permitted the use of methods that had not been attempted before, and that have not been attempted since: "[M]en and women were designated as 'assigned partners' and arbitrarily paired with each other to create 'assigned couples'." ==Four-stage model of the sexual response==