Cyto-morphological and enzyme-cytochemical investigations were carried out in five patients with lymphoreticular proliferations in the skin, using a simple smear technique. As purely morphological criteria allow only a limited differentiation of the infiltrate cells in the smears, enzyme-cytochemical methods were applied for further identification (detection of hydrolytic enzymes). With this new technique, the single cells are not damaged and keep their cell structure, so that the exact localisation of the enzyme activity is possible. Our investigations demonstrate the change of the cellular infiltration in the cutaneous smear during the clinical course of mycosis fungoides. In the premycotic stage, enzyme cytochemically positive monocytes and enzyme cytochemically negative lymphocytes with small nuclei are prevalent. In the infiltrative and tumor stages the cellular picture is dominated by polymorphonuclear lymphocytoid cells with medium sized nuclei, these cells contain ample amounts of esterases and acid phosphatase. In contrast to these findings, other lymphomas investigated by us are characterized by the lack of monocytes and an abundance of lymphocytes, which according to the stage of differentiation present a different pattern of the alpha-naphthylacetate-esterase and the acid phosphatase.