The analysis of cell surface markers with monoclonal antibodies has recently been developed and has been proved to be valuable in the diagnosis and classification of hematopoietic tumors. Occasionally, however, such serological studies have been shown to be inconclusive in identifying cell lineage and or clonal proliferation. In order to overcome these problems, two new approaches were introduced in our laboratory. First, T cell receptor and immunoglobulin gene rearrangement analysis as a means of immunomolecular marking was carried out. Second, a double immunoenzymatic staining technique for determining the surface phenotypes of proliferating lymphocytes using a monoclonal antibody against DNA polymerase alpha together with those detecting lymphocyte membrane antigens was developed. The results revealed by these techniques strongly suggested that some CD2-, CD5+, CD7+ ALL cases are of T cell origin and that AILD may be a neoplastic disease derived from either of the subsets of peripheral T cells.