A technique has been developed for achieving synchrony of division by selection for immediate pre- and post-fission cells of
Paramecium tetraurelia. Cell populations are fed granular tantalum, followed by density-gradient centrifugation. Dividing cells, which do not feed, are separated from feeding interphase cells. The selected cells are division-synchronous for at least two generations when resuspended in fresh culture fluid. This technique provides a rapid means of obtaining large numbers of synchronously dividing paramecia for cell-cycle studies and has general application for selective enrichment of non-feeding sub-populations of cells.