SUMMARY.—The nucleoside triphosphatase activity of epidermal Langerhans cells was studied in autolytic skin. Enzyme activity could be seen up to 2 days in specimens incubated at 37° C. and up to 26 days in specimens incubated at 4° C. It is pointed out that this histochemical staining method seems to be very stable and not confined to a special and transitory functional state of this cell system. It is concluded that this method could possibly be used as a marker for the identification of Langerhans cells underin vitroconditi