The cellular infiltrate in the dermis of incipient psoriatic lesions was qualitatively and quantitatively evaluated using cytochemical methods for the differentiation of inflammatory cells. The greatest intensity of the dermal infiltrate was always in the center of early lesions. It was shown that most of the inflammatory cells within the perivascular areas of the upper dermis were macrophages, monocytes and lymphocytes. The number of mast cells was not increased; eosinophils and plasma cells could not be detected. Only seldom could a single or a few polymorphonuclear leucocytes be seen in lesions at a more advanced stage. These findings are discussed in the light of known immunological and functional mechanisms.