AbstractWe have studied the nuclear DNA content of histologically favourable (n= 82) or unfavourable (n= 117) non‐Hodgkin lymphomas (NHLs) diagnosed between 1957 and 1978 in the Tampere University Central Hospital. The DNA analysis was done by applying a trypsin digestion method to archival tumour samples. DNA aneuploidy was seen in 40 per cent of the unfavourable cases and in 10 per cent of the favourable cases, but varied considerably between different histological subtypes. The unfavourable cases showed high proliferative activity (S‐phase fraction, SPF), while considerable variation in the SPF among the favourable NHLs was noted. Among the unfavourable NHLs, cases with DNA‐aneuploid tumours had significantly (P<0.01) worse prognosis than stage and treatment matched cases with DNA‐diploid tumours. In general, survival of the patients who had high SPF tumours was significantly lower compared with patients with low SPF tumours (P<0.01). However, SPF was not related to the prognosis in the unfavourable NHLs. We conclude that the flow cytometric DNA analysis revealed characteristic features in the favourable and unfavourable NHLs and may be useful in predicting the clinical outcome of p