Human sexuality researchers William H. Masters and Virginia E. Johnson (AP Photo/File)

Virginia E. Johnson, the female half of the Masters and Johnson scientific research duo that in the late 1960s redefined sex as a quantifiable, perfectible pleasure of human life to be pursued without guilt or fear, died July 24 in St. Louis. She was 88.

The cause was complications from heart disease, said her son, Scott Johnson.

Mrs. Johnson grew up on a Missouri farm, had no college degree and by the end of her career was nationally recognized as one of the most daring researchers of the postwar era.

Along with William H. Masters, her longtime research partner and onetime husband, Mrs. Johnson built on the groundbreaking work of Alfred C. Kinsey to erase the taboo surrounding human sexuality.

Kinsey, the author of the “Kinsey reports” on sexual behavior published in the late 1940s and early ’50s, had largely focused on personal accounts of sex for his work. Masters and Mrs. Johnson took a different approach: They took sex into a laboratory setting, where it could be studied with scientific rigor.

Virgina E. Masters in 1997 (AP Photo/James A. Finley, File)

Their findings, first published in 1966 in the best-selling book “Human Sexual Response” and later explored in volumes such as “Human Sexual Inadequacy” (1970), impressed academics and titillated a nation in the throes of the sexual revolution.

Of Masters and Johnson’s early readers, the oldest were born in the Victorian age. The youngest came of age in the era of Marilyn Monroe. Those not scandalized by the duo’s candid and technical discussion of masturbation, coitus and orgasms found a measure of comfort in the material. If the sexual act could be studied, then it could be improved, and problems such as impotence and frigidity could be cured like so many other afflictions of the human body.

In the mid-1950s, Masters was a gynecologist working in St. Louis at Washington University’s medical school on a study of sex that ultimately would include 694 volunteers — 312 men and 382 women ranging in age from 18 to 89.

His work would employ top-of-the-line technology, such as color movie cameras and electrocardiography. Research instruments reportedly included a Plexiglas phallus equipped with a camera that could document orgasms experienced by a woman.

The project was initially funded by the National Institutes of Health and later by private donors, including the Playboy Foundation. Masters instinctively understood that, to work, the project would need a woman with him at the helm.

“My attitude was,” Masters said, “that if you’re going into sex research, it is apparent that both sexes should be represented. No man is going to know very much about the human female, and no woman is going to know very much about the male.”

So it was that in 1957 he hired Mrs. Johnson, a former country singer and divorced mother of two who was looking for work while she studied sociology at Washington University.

At a time when many scientists did not consider sex a legitimate field of scientific inquiry, Masters risked his professional reputation to pursue the project. But by one interpretation, Mrs. Johnson risked even more. Ladies of her generation had not been brought up to discuss — much less seek — sexual satisfaction.

“I was never told about menstruation or anything,” she once told Time magazine. “There was a very rigid rejection of anything sexual. You didn’t talk about it.”

Over time, she ascended from assistant to co-director of the Masters and Johnson Institute, as it became known. She was said to have brought a more inviting, welcoming manner that compensated for Masters’s scientific bearing. She pushed for them to appear on television and in other mass media outlets such as Playboy and Redbook magazines, decisions that helped bring their work to an ever larger audience.

With Masters, Mrs. Johnson helped dispel notions that today might seem quaint if not ludicrous. Among them were misconceptions that the size of the male organ determined sexual prowess and that baldness was a marker of virility.

The pair showed that, surprisingly to some, a woman’s orgasm could last longer than a man’s. They debunked the idea that the elderly were consigned to lives devoid of sexual satisfaction.

Besides outraged moralists, their detractors included critics who resented the fact that “Human Sexual Response” seemed to overlook the mystical nature of love. The book was read by some, Time magazine wrote, to “suggest that good sex, like golf, is a matter of technique.”

Mrs. Johnson flatly denied that such was the intention. “I hope the whole mechanical myth will go down the drain,” she told Time. “I’m tired of it.”

In “Human Sexual Inadequacy,” she and Masters documented their treatment of hundreds of couples that struggled with dysfunction, including premature ejaculation and difficulty achieving climax. They reported a remarkably low 20 percent failure rate, a figure that critics in the scientific community found difficult or impossible to replicate.

But the Masters and Johnson brand had been forged. Their treatment of sexual dysfunction became, for a time, a dominant brand of sex therapy in America. The therapy included two weeks of intensive therapy and as many as five years of follow-up; about 70 percent of the program came from her ideas.

Mrs. Johnson, Masters said, had learned “more than any other woman in the world about human sexual function.”

Mary Virginia Eshelman was born Feb. 11, 1925, in Springfield, Mo. “I grew up with the sense,” she once told The Washington Post, “that accomplishment and talent were marvelous, but that marriage was the primary goal.”

She showed early promise as a singer, and she studied music, sociology and psychology. Her early jobs including stints as a radio country music singer, a newspaper reporter covering business, and a market research assistant for a CBS affiliate in Illinois.

With musician George Johnson, whom she married and later divorced, she had two children. Survivors include her son, Scott Johnson, and her daughter, Lisa Young, both of St. Louis; and two grandchildren.

Mrs. Johnson and Masters were married in 1971 and divorced in 1993. He died in 2001 at 85.

Their later books included “The Pleasure Bond” (1974), written with Robert J. Levin, and “Homosexuality in Perspective (1979). With Robert C. Kolodny, they wrote “Masters and Johnson on Sex and Human Loving” (1986). In 1988, also with Kolodny, they wrote “Crisis: Heterosexual Behavior in the Age of AIDS,” which U.S. Surgeon General C. Everett Koop criticized as “irresponsible” for what he called its use of “scare tactics” in addressing the spread of AIDS.

Mrs. Johnson said the work of destigmatizing sex would be long.

“We’ll need two generations,” she once told an interviewer, “who grow up believing that sex is honorable and good for its own sake, and not something to be kept hidden away in a jewel box to be taken down for festival occasions on Friday and Saturday nights.”