In order to define the characteristics of B-CLL cases in which the predominant cell population is composed of large lymphocytes, we studied 97 patients with B-CLL, comparing the cell morphological features with the clinical and biological findings and the immunological phenotype of the proliferating cells. Multivariant analysis showed that there were three significantly different morphological groups: Typical CLL, large lymphocyte CLL (LLL), and CLL with prolymphocytes (CLL/PL). The LLL group showed a greater incidence of lymphadenopathies (P less than 0.05) and higher percentages of both mu + delta + cells (P less than 0.01) and Fmc/7+ cells (P less than 0.001) than in typical CLL. The main differences between LLL and CLL/PL were the peripheral blood lymphocyte count and the percentage of Fmc/7+ cells (P less than 0.002)--both higher in the CLL/PL group--and the percentage of mouse rosette-forming cells (P less than 0.01)--lower in CLL/PL. Further studies including functional assays and survival analyses could contribute to elucidating whether these groups are different entities or a single disease with marked heterogeneity.