The results of nuclear DNA content analysis of a series of 28 patients with large cleaved follicular centre cell non-Hodgkin's lymphomas (NHL) are reported. DNA aneuploidy was found in 11 (39 per cent) cases. The DNA indices of the DNA-aneuploid peaks ranged from 1.14 to 2.28. Seven (25 per cent) cases were tetraploid. DNA ploidy was not associated with prognosis. The percentage of S phase cells (SPF) ranged from 2.0 to 30.5 per cent (median 5.1 per cent). Lymphoma patients with SPF higher than 9.7 per cent had a worse survival rate than patients with lymphoma with less than 9.7 per cent S phase cells but the difference did not reach statistical significance. The results of the DNA ploidy and SPF were comparable to those of intermediate and high grade malignancy NHLs.