Modification of the sperm penetration assay using human follicular fluid to minimize false negative results**Presented in part at the Thirty-Third Annual Meeting of the Society for Gynecologic Investigation, March 19 to 22,1986, Toronto, Canada, and the Forty-Second Annual Meeting of the American Fertility Society and the Eighteenth Annual Meeting of the Canadian Fertility and Andrology Society, September 27 to October 2,1986, Toronto, Canada.