The cytologic samples of 84 non-Hodgkin's lymphomas, classified according to the Rappaport system, were reviewed, with particular attention to the cell pattern, the size of the cells and other morphologic characteristics. The analysis revealed that: (1) the subgroups of malignant lymphoma in the Rappaport classification display a heterogeneous cytologic picture; (2) cytology cannot make the differentiation between nodular and diffuse non-Hodgkin's malignant lymphomas; and (3) reliable cytologic classification is possible only in certain cases of well-differentiated lymphocytic and diffuse histiocytic lymphomas. Well-differentiated lymphocytic lymphoma is characterized by a uniform cell picture consisting of mature lymphocytes, prolymphocytes or centrocytes up to 12 micron in size, by the presence of paraimmunoblasts and by the absence of reticulum cells. The diffuse histiocytic lymphoma contains over 48% centroblasts or over 8% immunoblasts or multinucleated giant blast cells.