Acute lymphocytic leukemias (ALLs) are morphologically classified into L1, L2, and L3. The former two types are phenotypically constituted of quite heterogeneous ALLs. In the present study, phenotypes of cells from five L3 type ALL were analysed in FACS-IV using a panel of monoclonal antibodies (MAbs). The leukemic cells of all these patients coexpressed la (HLA-DR), CD19, CD20, CD21, CD24, CD38, and surface immunoglobulins, whereas a negative reaction with MAbs CD1, CD2, CD3, CD4, CD7, CD8, and Ti (WT31), Ti gamma A, delta TCS 1, and anti TCR-gamma/delta was observed. Neither myeloid-monocyte-erythroid nor megakaryocyte related cell surface antigens were detected in these cases with L3 type ALL. Chromosomal analysis of the ALL cells from two cases revealed a normoploid karyotype with specific translocation t(8;14)(q24;q32), whereas it was normal (46XY or 46XX) for the remaining three cases. Expression of myc oncogene was high in the former group, but low in the later one. Basing from our findings, we conclude that L3 type ALL is heterogeneous with respect to immunophenotypes, cytogenetics and oncogene analysis.