Important insights into leukocyte differentiation and the cellular origin of leukemias have been achieved by the use of monoclonal antibodies for the detection of cellular antigens with impact on the diagnosis and classification of hematological malignancies. A successful rapid immunoenzymatic technique using application of microwave irradiation (MIWI) on bone marrow cells of various children with ALL is described. The MIWI-stimulated immunotyping of acute leukemia cells with a panel of monoclonal antibodies against differentiation antigens (i.e. CD2, CD7, CD10, CD19, CD20, CD24, HLA-DR and TdT) has been compared with the conventional APAAP procedure developed by Mason et al 1983. The commercial microwave oven we used operates at 2.45 GHz. Fifteen sec irradiation at 350 W during all incubation steps produced excellent color reactions with Fast Red TR and Fast Blue BB similar to the conventional immunoenzymatic method. The results so far have demonstrated that the application of the MIWI-technique eliminates the need for long incubation periods without loss of sensitivity. With this technique an immunological diagnosis of childhood leukemia cells is possible using air dried smears in an microwave oven within 30 minutes.