Paraffin-embedded lymph node biopsies from 107 patients with newly diagnosed non-Hodgkin's lymphomas were examined for cell DNA content and proliferative activity (as percentage of S-phase cells) by means of flow cytometry. Patients were diagnosed between 1975 and 1985 and were homogeneously treated according to the grade of histologic malignancy. Cytofluorimetric data were studied with regard to their correlation with histology (classified and reviewed according to both Kiel and Working Formulation criteria), clinical stage, presence of constitutional symptoms, presence of bulky disease, sex, age, and the following laboratory data measured at diagnosis: erythrocyte sedimentation rate, hemoglobin, serum lactic dehydrogenase and serum albumin concentration. Aneuploidy was more frequent in the high grade malignant subtypes and in the miscellaneous group but showed no correlations with the other clinical parameters studied. Proliferative activity demonstrated a wide variation of data but a trend was evident toward higher proliferative values in the more severe histologic subtypes. The survival discrimination allowed by high- and low-grade malignant histology is exactly reproduced when highly and slowly proliferating lymphomas are considered (greater than or less than or equal to 12% of S-phase cells). These results, analyzed with those in the literature, suggest that measurements of ploidy and proliferative activity add little independent information to what is already provided by current histologic classifications, mainly as far as clinical evaluation and prognosis are concerned. Cytokinetic-aided therapeutic choices can be usefully proposed in a restricted number of cases. Improvement of the available lymphoma classifications through a better integration of ploidy and cytokinetic data with immunologic, genetic and histologic findings is still an object to be pursued in cytometric studies.