The capacity of epidermal cells (EC) to present antigen to primed and non-immune T cells was investigated using a culture system that supports antigen-specific primary and secondary proliferative responses. Although both naive and bovine serum albumin (BSA)-immune T cells reacted against BSA in the presence of either splenic or epidermal antigen-presenting cells (APC), important differences were noted in the kinetics and the magnitudes of the various responses. Most conspicuous was the relatively poor primary response supported by EC which evidently elicited very few BSA-immune T-helper cells. Despite this, the primed antigen-specific T cells recovered were phenotypically similar to those resulting from the stronger primary responses induced by spleen cells. In contrast to this disparity in the ability to prime, EC and spleen cells stimulated secondary reactions of comparable magnitude. We therefore consider that, in comparison with splenic APC, EC may require some additional stimulus to acquire the capacity to prime.