Abstract: Growth of keratinocytes is provided by subjecting a basal medium, insulin, pituitary compound and keratinocytes to cell growth conditions. Cell growth can be provided in the absence of exogenous epidermal growth factor. A conditioned medium results after the keratinocytes are subjected to cell growth conditions, treated keratinocytes are provided, and the treated keratinocytes are subjected to cell growth conditions in a basal medium. The conditioned medium contains autocrine factor. The conditioned medium then is contacted with further keratinocytes to provide a cell growth mixture. The cell growth mixture is subjected to incubation in order to provide replicative DNA synthesis and hence cell proliferation. Cells so provided can be used for dermatological research, toxicological testing and skin grafts.