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 less than 0.0001). High S-phase rates were associated with a poor prognosis within the whole material (p less than 0.01) and within the group of 'high grade' NHL (p less than 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 less than 0.05). In multivariate analyses, the S-phase rate gave, in several subgroups, independent prognostic information, besides clinico-pathological variables.