The actin cytoskeleton is a remarkably dynamic structure in non-muscle cells which responds to cell stimulation by a variety of cytokines. A paradigm for such cytokine-induced reorganization of the actin superstructure is the actin response to growth factor of the EGF/PDGF family. This paper reviews the role of the polyphosphoinositide-metabolism, small GTP-binding proteins and profilin in the reorganization of the actin cytoskeleton in cells activated by growth factors.