We have analyzed DNA content and proliferative activity in morphologically defined cell subpopulations of 74 non-Hodgkin's lymphomas (NHL) and 29 reactive lymph nodes using DNA image cytometry and antibodies to proliferative markers (proliferating cell nuclear antigen (PCNA) and Ki67). Thirteen (18.6%) of 70 NHL cases were aneuploid. The follicular center cell-derived lymphomas with DNA aneuploidy had DNA indices (DI) predominantly in the tetraploid region, whereas aneuploid high-grade (HG) NHL presented DNA histograms with multiple aneuploid stemlines. In aneuploid centrocytic-centroblastic (CB/CC) NHLs, DNA aneuploidy was found exclusively in centroblasts, whereas centrocytes in these cases were diploid. Percentages of cells in S and G2/M phase in chronic lymphocytic leukemia (CLL), immunocytoma (IC), centrocytic NHL (CC), and centrocytes from CB/CC were low (< 5%), whereas the respective values for centroblasts in CB/CC and in malignant cells of HG NHL were similar to those of large lymphoid cells in the reactive lymph nodes (mean, 39.5%, 36.6%, and 53.5%, respectively). The mean percentage of PCNA positive cells in CLL, IC, and CC was 4.9%. In the follicles of CB/CC NHLs there was, on average, 56.9% of PCNA positive centroblasts and 8.1% of PCNA positive centrocytes. In HG NHL, the mean percentage of PCNA positive lymphoma cells was 27.9%. A positive correlation was found between percentages of cells in S and G2/M phase and cells positive for PCNA (P < 0.001). There was also a significant correlation between percentages of Ki67 (mean, 19.2%) and PCNA positive cells (mean, 17.7%) (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)