Prevention of the postcoital luteinizing hormone surge by ultrashortloop feedback control*†*Recipient of the Squibb and Sons Award for Outstanding Research. Presented at the Twenty-Ninth Annual Meeting of the Pacific Coast Fertility Society, October 14 to 18, 1981, Palm Springs, California, and at the Thirty-Eighth Annual Meeting of The American Fertility Society, March 20 to 24, 1982, Las Vegas, Nevada.†Supported in part by the National Institutes of Health (grant 5P39 HD 10202 Bioassay Core).