Among several monoclonal antibodies (moABs) directed against human interleukin 2 (IL-2), the 15-2 moAB raised in our laboratory against unglycosylated recombinant IL-2 (produced in Escherichia coli) cross-reacted with a human skin epitope. This moAB gave a strong staining on the cell-surface membranes of keratinocytes from the granular layer of the epidermis. In addition, the 15-2 moAB stained 15% of epidermal cell suspensions obtained from suction blisters and reacted with cells from the spinous layer in parakeratosis and psoriasis, as well as with spinous epithelioma cells. Preincubation of the 15-2 moAB with pure human recombinant IL-2 abrogated skin binding, whereas a polyclonal antikeratin antiserum did not block 15-2 skin binding. Two other anti-IL-2 moABs, one directed against unglycosylated recombinant IL-2 (17-2 moAB) and one against glycosylated natural IL-2 (9B11 IE5 moAB), were unreactive on skin. Taken together, the data suggest that the 15-2 moAB binds to an epitope cross-reacting with, but different from, IL-2 which is located in the cell-surface membranes of granular layer cells. This cross-reactive epitope may provide a useful probe for the study of human epidermal cell differentiation.