A scoring system, based on the immunophenotypic analysis of a panel of five membrane markers (CD5, CD22, CD23, FMC7, SmIg) was shown to be useful in the distinction between chronic lymphocytic leukemia (CLL) and other B-cell lymphoproliferative diseases (non-CLL). We investigated whether the monoclonal antibody SN8 (CD79b) could improve our previous scoring system. Peripheral blood samples of 298 patients with CLL and 166 patients with non-CLL were analyzed by flow cytometry. Using the five standard markers, the accuracy of the scoring system was 91.8%, using a cutoff of 4 points or higher, to distinguish CLL from non-CLL. This was increased to 96.6% if SN8 was added and a cutoff of 4 points or higher was also used. A similar accuracy, 96.8%, was observed if CD22 was excluded and a cutoff of 3 points or higher was used. Thus, the replacement of CD22 by SN8 in the original scoring system significantly increases its potential to discriminate between CLL and other B-cell lymphoproliferative diseases.