Dr. William Masters, who with his partner Virginia Johnson changed the way Americans think about sex, had a romantic side. Geraldine Baker Masters, his wife since 1993, recalls the conversation she had with him in a Tucson hospice just before his Feb. 16 death at age 85 from complications of Parkinson's disease. "His last words to me were, 'You're a knockout,' " she says with a laugh.

Masters and Johnson built upon the work of '40s sex researcher Alfred Kinsey. But while Kinsey used interviews, they used cameras, electrocardiographs and electroencephalographs to record the intimate behavior of 694 men and women. Never before had the sex act been examined in such detail. Nor had sex researchers been asked to appear on The Tonight Show. "I told them we'd go on if they agreed not to wedge us between Jackie Mason and a baton twirler," says Johnson, 76, who became Masters's second wife (and added his surname) in 1971.

A Cleveland native, Masters came to sex research in 1954 after a decade as an obstetrician-gynecologist in St. Louis. Johnson, then a divorced mother of two, became his assistant in '57 (Masters also had two children with his first wife). Though Johnson had planned to pursue a graduate degree in anthropology, whenever she threatened to leave, she says, "he kept coming up with new projects." But Masters, whom Johnson describes as "driven," could also be difficult, and the couple split in 1992.

Although written in the dry language of science, their Human Sexual Response, published in 1966, became a surprise bestseller—as did a 1970 sequel. "Dr. Masters's contribution," says Dr. Mark Schwartz, director of the Masters and Johnson clinic in St. Louis, "was to bring sexuality out of the closet."