Extensive animal data suggest that prostaglandins are involved in the epidermal induction of ornithine decarboxylase (ODC). We undertook this study to investigate their role during induction of hyperproliferation in human skin. Topical indomethacin (Elmetacin) or vehicle only were applied under occlusion on the backs of healthy volunteers. This was followed 1 h later by Sellotape stripping and biopsies were carried out for the estimation of the levels of ODC. There was no significant difference in the level of ODC in the indomethacin-treated and control sites. Also, test sites were irradiated with 3 MEDs of UVB, and this was immediately followed by the application of indomethacin or vehicle only on the irradiated sites. After 8 h biopsies were taken and the levels of ODC were again similar in both sites. The data indicate that the cyclo-oxygenase products in human epidermis do not contribute to the induction of ODC.