Levels of cholesterol and phospholipids in freshly ejaculated sperm and Percoll-gradient-pelletted sperm from fertile and unexplained infertile men*†‡*Supported by a grant from the Ottawa General Hospital Research Fund, Ottawa, Ontario, Canada.†Supported by the Prachatipoke Foundation, Bangkok, Thailand (p.s.).‡Presented at the 46th Annual Meeting of The American Fertility Society Meeting, Washington, D.C., October 13 to 18, 1990.