Masters and Johnson were a pioneering team in the field of human sexuality, both in the domains of research and therapy. William Howell Masters, a gynecologist, was born in Cleveland, Ohio in 1915. Virginia Eshelman Johnson, a psychologist, was born in Springfield, Montana in 1925. To fully appreciate their contribution, it is necessary to see their work in historic context. In 1948, Alfred C. Kinsey and his co-workers, responding to a request by female students at Indiana University for more information on human sexual behavior, published the book Sexual Behavior in the Human Male. They followed this five years later with Sexual Behavior in the Human Female. These books began a revolution in social awareness of and public attention given to human sexuality. At the time, public morality severely restricted open discussion of sexuality as a human characteristic, and specific sexual practices, especially sexual behaviors that did not lead to procreation. Kinsey's books, which among other things reported findings on the frequency of various sexual practices including homosexuality, caused a furor. Some people felt that the study of sexual behavior would undermine the family structure and damage American society. It was in this climate - one of incipient efforts to break through the denial of human sexuality and considerable resistance to these efforts - that Masters and Johnson began their work. Their primary contribution has been to help define sexuality as a healthy human trait and the experience of great pleasure and deep intimacy during sex as socially acceptable goals. As a physician interested in the nature of sexuality and the sexual experience, William Masters wanted to conduct research that would lead to an objective understanding of these topics. In 1957, he hired Virgina Johnson as a research assistant to begin this research issue. Together they developed polygraph-like instruments that were designed to measure human sexual response. Using these tools, Masters and Johnson initiated a project that ultimately included direct laboratory observation and measurement of 700 men and women while they were having intercourse or masturbating. Based on the data collected in this study, they co-authored the book Human Sexual Response in 1966. In this book, they identify and describe four phases in the human sexual response cycle : excitement, plateau, orgasm, and resolution. By this point in time, the generally repressive attitude toward sexuality was beginning to lift and the book found a ready audience. Masters and Johnson were quickly catapulted to celebrity status as their book became a best seller. During this period, Masters divorced his first wife and Masters and Johnson wed. In 1970, they published Human Sexual Inadequacy, which was concerned with the treatment of impotence, premature ejaculation, frigidity and other sexual problems. In the wake of these two publications, the field of sex therapy -- the clinical treatment of sexual problems -- was born. Throughout the 1970s and 1980s, Masters and Johnson continued their research and publication efforts. Their book Homosexuality in Perspective, which described the sexual responses of gay men and lesbians, was published in 1979. In this book, Masters and Johnson debunked the notion that homosexuality is a mental illness. However, their claimed ability to change the sexual preferences of homosexuals who wished to change produced considerable criticism from the gay community and from other sex researchers. Their final collaboration, Heterosexual Behavior in the Age of AIDS, published in 1988, was not well received because of its criticism of the general need for safer sex practices (including condom use) in heterosexual relationships. In the early 1990s, Masters and Johnson were divorced and their over 30-year collaboration in sex research and therapy came to an end. In 1970, based on their studies of problems in sexual fulfillment, Masters and Johnson established a clinic for the treatment of sexual problems in St. Louis. Many of the students who trained at their center went on to establish practices in sex therapy around the country. Additionally, many of the therapeutic practices begun at the clinic, such as assisting couples to more fully experience and focus on basic physical sensations, are central to contemporary sex therapy nationwide. One of the key issues of concern to Masters and Johnson was the issue of impotence. In Human Sexual Inadequacy, Masters and Johnson maintained that 90 percent of impotence--the persistent inability to achieve or maintain an erection -- is psychological in origin. Even in older men, according to Masters and Johnson, emotional issues rather than organic problems are the main causes of impotence. Further research and improved medical testing since their claim has shown impotence caused purely by psychological issues to be closer to 40 percent to 50 percent. Masters and Johnson noted that having several experiences of impotence could cause men to withdraw from sexual activity entirely in an attempt to avoid the frustration and embarrassment of being unable to achieve or maintain an erection. Inadequate communication and fear related to only talking about sexual issues complicates the problem of male impotence, as well as female orgasmic inadequacy. However, Masters and Johnson reported great success in treating impotence, especially when it had its roots in fear of failure and performance anxiety. Masters and Johnson also studied and therapeutically addressed the problem of premature ejaculation. They found that the subjects in their studies had internalized a middle class culturally constituted fear of being unable to control the ejaculatory process sufficiently to satisfy their female partners. Working class men, they discovered, were not as concerned with partner satisfaction. As had Kinsey before them, Masters and Johnson confirmed the near universality of masturbation in their subjects. The sex therapy program developed by Masters and Johnson attempts to help clients by providing appropriate sex information, alleviating anxiety about sexual performance, and facilitating verbal, emotional, and physical communication with sex partners. Thirty years since their first study was published, the contributions of Masters and Johnson on sexual functioning, sexual problems and therapeutic interventions for these problems remains among the most significant work in these areas. While some of their work generated considerable skepticism or outright criticism, they helped to revamp contemporary thinking about sex, including assisting in moving society toward a more open discussion of sexual practices and experiences.