Tumour S-phase fraction, but not the apoptotic fraction, had prognostic value in 92 patients with B-cell non-Hodgkin's lymphoma (P < 0.0001 and P = 0.85 respectively). Multivariate analysis showed that S-phase fraction was the strongest prognostic indicator in all cases (P = 0.0003, relative risk 4.3; age: P = 0.16; grade: P = 0.81), as well as in the 63 primary biopsy cases (P = 0.0006, relative risk = 7.3; international prognostic index: P = 0.015, relative risk = 3.2; B symptoms: P = 0.017, relative risk = 3.3; bulkiness: P = 0.65; grade: P = 0.91).