The aim of this work is to study and compare lipid composition of peritoneal and ovulatory follicular fluid of women. The studied patients are involved in a FIV protocol. We have studied 53 peritoneal fluids and 90 follicular fluids from 33 patients. On each sample the following parameters are estimated: cholesterol, triglycerides, phospholipids, non esterified fatty acids (A.G.N.E.), HDL and LDL cholesterol, HDL and LDL phospholipids. Lipid composition of follicular and peritoneal fluids differ from these of blood plasma. The two mediums studies show no differences with regard to their lipid composition. In both cholesterol is only found as HDL cholesterol. Cholesterol arising from spermatozoa membranes may be implicated in capacitation phenomenon. HDL Cholesterol, the only form found in the studied mediums, may act as a cholesterol acceptor. Theses two points partially explain the fact that follicular and peritoneal fluids are good mediums for capacitation and survival of spermatozoa.