Immunophenotyping of peripheral blood lymphocytes from 95 patients with B-cell chronic lymphocytic leukemia (B-CLL) was performed to estimate surface membrane intensity of the HLA-DR, CD20, and light-chain antigens. Cases were classified as having weak, moderate, or strong intensity by a standard slide immunocytochemical method, and the fluorescence intensity (FI) was measured by flow cytometry in molecules of equivalent soluble fluorescence (MESF). Staining intensity was strongest for HLA-DR; with both methods, 94 cases were classified as strong. For CD20, 67% were weak, 27% moderate, and 6% strong; the mean MESF values were 31.7, 66.4, and 177.4 x 10(3), respectively (P < .001). Thirty-nine percent had weak surface light-chain staining, 50% moderate, and 11% strong; the mean MESF values were 4.9, 7.5, and 16 x 10(3), respectively (P = .005). These results indicate that the FI of cell surface antigens can be estimated and quantified by flow cytometry. Because of the wide overlap of FI values among the three groups, an exact correlation was not found between the two methods of classifying intensity of surface antigen expression. The usefulness of these quantitative measurements needs further analysis in clinical trials.