The prognostic relevance of flow cytometric DNA measurements of lymph node biopsies in relation to histopathology according to the Kiel classification, stage, age and presence or absence of B‐symptoms was investigated in 106 patients with non‐Hodgkin lymphomas (NHL) of proven B‐cell type. Biopsies were taken at diagnosis before treatment. The mean proportion of cells in S‐phase was significantly lower in the 76 patients with a ‘low grade’ NHL (4.4 per cent) than in the 30 patients with a ‘high grade’ NHL (13.0 per cent) (p<0.0001). High S‐phase rates were associated with a poor prognosis within the whole material (p<0.01) and within the group of ‘high grade’ NHL (p<0.05). In the subgroup CB‐CC lymphomas of ‘low grade’ NHL, the prognostic value of the S‐phase rate was stronger than any other investigated parameter (p<0.05). In multivariate analyses, the S‐phase rate gave, in several subgroups, independent prognostic information, besides clinico‐pathological variables. Copyright © 1990 John Wiley & Sons, Ltd