The distribution of lysophosphatidylcholine, lyso-platelet-activating factor and platelet-activating factor (PAF) was studied in human plasma and in follicular and peritoneal fluid. In plasma, peritoneal and follicular fluids, 51%, 87% and 89%, respectively, of the total lipids were found in the protein fraction (the density > 1.21 fraction). Two forms of lysophospholipids were identified in this fraction: one of high affinity and one of low affinity for albumin. The metabolism of PAF in human follicular fluid, peritoneal fluid and plasma was also investigated. PAF-acetylhydrolase activity was found in both peritoneal and follicular fluids which induced a time-dependent hydrolysis of [3H]PAF. The half-life of PAF was estimated to be 7-12 min in plasma, 15-25 min in peritoneal fluid and approximately 2 h in follicular fluid. PAF-acetylhydrolase activity in embryo culture media supplemented with 10% serum was markedly inhibited by addition of commercial serum albumin. When 25 g albumin l-1 was added, 22% of [3H]PAF was hydrolysed h-1 compared with 72% in media without albumin. The concentrations of lysophosphatidylcholine measured in plasma, in follicular and peritoneal fluids were 252, 286 and 53 mumol l-1, respectively. The distribution of these lysophospholipids and the metabolism of PAF in the female genital tract fluids reported in the present study provide evidence for the involvement of these biologically active lipid mediators in a variety of reproductive processes including sperm-egg interactions and embryonic development.