Follicular fluid is made of both follicular cell-secreted molecules as well as blood infiltration into the follicle. Sperm-attracting activity has been associated to column-filtered proteins as well as to progesterone. Here we report the initial characterization of a protein with this activity. Follicular fluid was collected from preovulatory follicles in freshly obtained ovaries from a local slaughterhouse. Fluid was cleared from cells and fractionated by size exclusion chromatography and polyacrylamide gel electrophoresis. For gamete interaction, sperm were allowed to swim in an agarose-covered slide designed to separate two wells by a rod in a fixed pattern. At each well, a semisolid agarose solution containing either the attractant with oocytes or control solution in one end, whereas capacitated boar sperm was at the opposite well. Sperm bound to oocytes were evaluated under phase contrast microscopy. Results show that fluid from preovulatory follicles have a sperm attracting activity and that this activity can be associated with an 8600 Dalton protein that at the N-terminal end exhibit close relation to Apoliprotein B2.