The clinical utility of the indirect immunofluorescence (IF) and the alkaline phosphatase-anti-alkaline phosphatase (APAAP) techniques was compared in 103 newly diagnosed acute leukaemia patients immunophenotyped using a panel of 19 monoclonal antibodies (MoAb). In spite of slight variations in the percentages of cells reacting with particular MoAbs when comparing the two methods we found no discrepancies in the final classification of each case. In ANLL (n = 73) the best correlation between the two methods was found for CDw65 which is a good screening marker, and for CD15 having a prognostic significance. In ALL (n = 30) the best correlation was observed for CD19 and CD10, both of great diagnostic importance. The following antigens present both in membrane and in cytoplasm displayed higher positivity with the APAAP than in IF HLA-Dr, CD71 and CD11b in ANLL, CD22 and HLA-Dr in nonT-ALL and CD3 in T-ALL. The important advantages of the APAAP technique are: 1) its use with routinely performed bone marrow or peripheral blood films, which can be stored before staining, 2) the possibility of correlating morphology with immunological characterization and documentation of the results.