Peripheral blood T and B cells were enumerated in 26 normal adults by conventional immunological markers (erythrocyte rosette and surface membrane immunoglobulin) and by monoclonal markers (T11 and B1) using both membrane immunofluorescence of cells in suspension and immunoperoxidase staining of dried, fixed, cytocentrifuged cells after separation from blood by buoyant density centrifugation. The results of immunochemistry were determined independently from the results of erythrocyte rosetting and membrane immunofluorescence techniques. A high correlation was found between all three methods for enumerating T cells (erythrocyte rosetting, T11/immunoperoxidase, and T11/indirect immunofluorescence). Correlation was less good between the results of the three methods for enumerating B cells; surface membrane immunoglobulin and B1/indirect immunofluorescence techniques showed the highest correlation. The results suggested that B cells may be preferentially lost during the extensive cell washings entailed in the indirect immunofluorescence procedures. Immunochemical methods, using monoclonal antibodies, are useful for enumerating lymphocyte subsets in blood, particularly when permanent records are desired.