Over a period of twelve years Masters and Johnson observed and recorded more than 10,000 male and female orgasms. Dr. Masters began his programme of sex research in 1954 after specialising for many years in gynaecology and hormone replacement therapy for postmenopausal women. He found his assistant, Mrs. Virginia Johnson - now Mrs. Masters through an advertisement. Their first subjects were prostitutes - eight female and three male - but gradually they collected non-professional volunteers: their final sample was 694 individuals.