Abstract: A method of identifying highly fecund males in which an isotonic, buffered liquid test specimen of semen is layered on top of a barrier medium that inhibits net movement (migration) of less mobile sperm into the barrier medium. Differences in mobility of populations of sperm among test subjects have been found to predict whether a male will be highly fecund or not. Sperm migration into the barrier medium is quantitated, for example by analyzing the barrier medium in a spectrophotometer or a photometer after sperm migration is allowed to occur. Alternatively, a collection member coated with a sperm binding protein may be placed below the barrier medium, and the number of sperm that bind to the collection member quantitated after incubation. The invention also includes a device for incubating the barrier medium at a physiologic temperature for a sufficient period of time to allow the highly mobile sperm to migrate into the barrier medium.