We have isolated, by subtractive and differential hybridization from a library constructed from keratinocyte colony-forming cells (K-CFCs), a cDNA coding for the rat CD24 (nectadrin, heat stable antigen). CD24, a glycoprotein thought to be involved in cell-cell adhesion and signalling, is highly expressed in keratinocytes located in the bulge area of the rat vibrissa which contains the most K-CFCs. CD24 is also expressed in the outer epithelial sheath of human hair follicles and in glabrous epidermis. However, its expression is not restricted to K-CFCs as demonstrated by cell sorting experiments, and it is thus not a specific marker of clonogenic keratinocytes. Rather, its preferential distribution in keratinocytes located in the most innervated area of the rat vibrissal follicle, i.e., the bulge, suggests that is function could be related to the tactile role of the hair follicle.