Aims-To detect cytoplasmic and nuclear antigens using flow cytometry in acute leukaemia and to use this technique for double marker combinations.Methods-Cytoplasmic staining was carried out in samples from 40 cases of acute leukaemia with monoclonal antibodies against the myeloid antigen CD13, the lymphoid antigens CD3, CD22, p chain and the enzymes terminal deoxynucleotidyl transferase (TdT) and myeloperoxidase (MPO We describe a technique that does not disrupt the cells and preserves both antigen expression and light scatter, and permits a precise study of the leukaemic cells by gating the desired population for analysis. MethodsPeripheral blood and bone marrow anticoagulated samples from 40 patients with acute leukaemia at presentation or relapse were studied. The diagnosis was based on morphology and cytochemistry according to the FAB criteria.8 9