The results of cytogenetic studies are reported in 89 patients with B-cell CLL. LPS (E. coli lipopolysaccharide), PWM (pokeweed mitogen), PHA (phytohaemagglutinin), EBV (Epstein-Barr virus), TPA (phorbol 12-myristate 13-acetate), and LA (leucoagglutinin) were used as mitogens. Mitoses were obtained from 78 cases. Clonal aberrations could be demonstrated in 26 cases. Trisomy 12 was the most frequent finding (8 cases) and was sole abnormality in 4 cases. Chromosomes #14, #17, and #11 were involved in structural aberrations in 5, 7, and 7 cases respectively, but a t(11;14)(q13;q32) was the only structural aberration seen more than once. The median observation time was 47 months (range 1-87). The presence of clonal abnormalities did not influence survival significantly, either when calculated from diagnosis or from cytogenetic analysis. Patients with more than one aberration, however, had a significantly shorter survival than patients with normal mitoses only (p less than 0.05). The survival of 8 patients with trisomy 12 (in 4 as sole abnormality) was not different from that of patients with normal mitoses only.