Replica plating, i.e., the production of multiple copies of a pattern of colonies derived from single cells, can now be applied to human cell lines using polyester mesh as a substrate. In searching for somatic cell mutants, often the only means of identifying a mutant clone is an assay that leaves the selected cells nonviable. With replica plating it is possible to retrieve that clone from the corresponding position on the replica. In addition, DNA from the colonies on the polyester replica can be transferred to nitrocellulose, facilitating the identification of clones using radioactive tracers or DNA probes.