Recently there have been numerous studies of testicular cells which have used velocity sedimentation for several hours at 1g to separate the cells. In most cases these cells have been identified by their velocities of sedimentation rather than by their morphologic characteristics. Using velocity sedimentation at 55g for 21 minutes in a previously described isokinetic gradient of Ficoll in tissue culture medium, modal populations of mature sperm cells, red blood cells, spermatids with perforatoria, multinucleated cells and other round nucleated cells were separated from suspensions of testicular cells primarily according to differences in diameter. While these modal populations of morphologically identified cell types were well defined, they were frequently in overlapping zones of the density gradient and not widely resolved from each other.