Langerhans' cells were enumerated in the skin of eight borderline and tuberculoid leprosy patients by the enzymatic histochemical demonstration of ATPase in these cells in epidermal sheets. The number of Langerhans' cells was significantly reduced in the skin lesions of these patients compared with normal appearing skin from the same patients. The morphological details of these cells were not clear under light microscopy; further study with electron microscopy is desirable.