Cultured epithelial grafts are used in the clinical treatment of both non-healing and acute partial-thickness wounds, owing to their ability to stimulate endogenous re-epithelialization. We have previously demonstrated that during the first 24h following plating, human epidermal keratinocytes secrete an autocrine-acting mitogenic activity. Since the biological activity of cultured grafts is believed to decrease with cellular age, the effect of both in vivo andin vitro keratinocyte age on the secretion of this mitogenic activity, as well as on responsiveness to this activity, was studied. Keratinocytes from donors ranging in age from 2 to 81 years were analysed at increasing in vitro population doublings. Secretion into the medium of the mitogenic activity was not affected by either in vivo or in vitro cellular ageing, while responsiveness of keratinocytes to this mitogenic activity was age-related. These results suggest that cultured grafts from elderly donors may be effective in wound treatment.