"When in 1953 Gregory Pincus approached Rock about collaborating on a study of the contraceptive effects of progesterone, Rock unhesitatingly signed on. The two scientists had known each other since the 1930s and closely followed each other’s work. Rock’s finding, in the course of his research on in-fertility treatments, that small amounts of female hormones inhibited ovulation, helped validate Pincus’s similar results in animal trials. Pincus needed someone with Rock’s clinical experience to ex-tend research trials to human subjects. And it helped in terms of fund-raising and public relations that Rock had an unimpeachable reputation as physician and medical researcher. Their cooperative work was made possible by an influx of funds from Katharine Dexter McCormick, whom Sanger had convinced to support Pincus’s promising research. Starting in the summer of 1953, McCormick began to immerse herself in the project and sent regular progress reports to Sanger mentioning Rock’s involvement. In November 1953 McCormick informed Sanger that Rock and Pincus had begun the first human trials in the study. But Sanger, who was preoccupied with setting up the International Planned Parenthood Federation (IPPF), did not appear to be aware of the extent of Rock’s participation. Nor did she feel completely comfortable with his involvement."