In a previous report we showed that D47 CD1a monoclonal antibody positively labelled B-CLL cells of some patients. Six cases were selected to further characterize CD1 antigenic expression at the leukaemic cell surface using flow cytometry with a battery of six CD1a, two CD1b and two CD1c monoclonal antibodies. CLL cells were positively labelled with CD1a antibodies except OKT6 and NA1/34; in all cases they were CD1b negative and CD1c positive. These results suggested that CD1a, c epitopes can be detected on leukaemic B cells in addition to other T cell differentiation antigens. In view of recently published data demonstrating the presence of CD1c molecule in normal B cell subsets, our results further question the relationship of B-CLL with a restricted subpopulation of B cells.