In a material of 80 patients with non-Hodgkin lymphoma a multivariate analysis was carried out taking the following variables into account: Age, clinical stage, B-symptoms, morphologic diagnosis and fraction of S-phase cells in the tumour determined by flow cytometry. Clinical stage, proportion of cells in the S-phase, and age of the patient were significant independent prognostic factors. Morphologic malignancy grade and B-symptoms were not significant parameters in this analysis. It was concluded that DNA analysis with determination of the fraction of S-phase cells is a valuable complement to morphology in the evaluation of patients with non-Hodgkin lymphoma. In combination with the clinical stage it gives very good discrimination into groups with different prognoses.