AbstractThe finely tuned mechanisms that control cell cycle progression go awry in cancer, pointing to proto‐oncogene products as important players in cell‐cycle regulation. One such proto‐oncoprotein, c‐Src, has previously been directly implicated, based on its requirement for growth factor‐stimulated DNA synthesis. Rocheet al.(1)have now shown that c‐Src or its close relatives are also required for cell division to occur. The demonstration of essential functions for the Src family at multiple points in the cell cycle raises important questions about the normal and transforming activities of these and other proto