Blood mononuclear cells from 540 newly diagnosed, unselected patients with B-cell chronic lymphocytic leukemia (CLL) were examined by immunofluorescence flow cytometry for a panel of surface membrane markers, including IgM and IgD, the monoclonal antibodies anti-CD3, -5, -20, -21, -22, -FMC7, and, for the final 125 patients, anti-CD23. There were 503 CD5+ and 37 CD5- cases. In the CD5+ cases, the cells typically expressed IgM, IgD, CD20, CD21, CD22, and CD23. In univariate analysis, age, clinical stage, IgM-fluorescence intensity, CD23, and FMC7 had significant prognostic importance, with high IgM-fluorescence intensity, high FMC7, and low CD23 expression being associated with a short survival. There was no significant difference in survival between 351 cases expressing IgMD and 55 cases expressing IgM without IgD, or between kappa and lambda light chain monoclonal cases. CD20, CD21, and CD22 had no prognostic importance. In Cox multiple regression analyses, age, CD23, IgM-fluorescence intensity, and clinical stage (International Workshop System) had independent prognostic importance. Thus, besides clinical variables, CD23 and IgM intensity might be useful prognostic markers in the management of CD5+, B-cell CLL. The survival of CD5- patients was on the borderline of being significantly shorter than that of CD5+ patients. The majority of the CD5- cases were FMC7+, CD23-, had strong IgM fluorescence, and had splenomegaly.