A black woman with chronic lymphocytic leukemia (CLL) was found to have monoclonal B lymphocytes with one type of surface immunoglobulin and one variant of G6PD (glucose-6-phosphate dehydrogenase) (G6PD A). Erythrocytes and T cells contained both G6PD A and G6PD B and hence were of polyclonal origin. The CLL cells in this patient likely arose from a developmental stage later than the step of differentiation into T and B lymphocytes. Furthermore, her erythrocytes did not arise from a stem cell affected by the CLL process.