Leading Sexuality Researcher Dies ST. LOUIS (AP) -- Dr. William H. Masters, one of the first and leading researchers in the field of human sexuality, died in a Tucson, Ariz. hospital Friday of complications from Parkinson's disease, a hospital spokeswoman said. He was 85. Masters gained an interest in sexuality while a medical student in New York in the 1940s. He established himself as a researcher in obstetrics and gynecology and moved on to study human sexuality at Washington University in St. Louis, where he co-founded the Masters and Johnson Institute. Partnered with Virginia Johnson, his future wife, Masters conducted interviews and observed sex in the act, researching biological responses and monitoring the physiology of sexual arousal. Based on that research, the pair published ''Human Sexual Response'' in 1966, which became a best seller despite its technical language. ''He was pioneering in a neglected area and was willing to risk, even enjoyed risking, his professional existence by breaking through in a field that was avoided and a source of a lot of discomfort,'' Virginia Johnson Masters told the St. Louis Post-Dispatch newspaper. The couple published several more books and worked together until 1992. They divorced a year later. Masters continued to live in St. Louis until 1994, when he retired at the age of 78. He is survived by his third wife, Geraldine B. Masters, a daughter, son and brother. A family service is planned in Tucson. AP-NY-02-18-01 0044EST< http://www.newsday.com/ap/national/ap565.htm *************