The great majority of childhood lymphoblastic leukaemias are identified by monoclonal antibodies as neoplasias of the B‐cell progenitor compartment

36 acute leukaemias in children, 24 lymphoblastic and 14 myelogenous, have been examined with a set of 10 monoclonal antibodies by indirect fluorescent staining. In the lymphoblastic group the leukaemic cells of 4 children were found to have T-cell phenotype, while 19 of the other 20 T-cell phenotype negative cases were found to be positive for the c-ALL antigen. All 20 were negative for surface immunoglobulin as well as cytoplasmic mu-heavy chains. However, 17 (85%) reacted positively with the monoclonal antibody AB-1 which we have developed against a B-cell lymphoma, thus revealing B-lineage specificity. Another B-lineage-associated antibody (AB-2) reacted with 8/20 (40%) of the cases with distribution similar to B-1. These findings suggest that the great majority of non-T-non-B acute lymphoblastic leukaemias are neoplasms derived from the B-cell progenitor compartment. Moreover, monoclonal antibody testing allows further sub-categorization in this group. Similarly the acute-myelogenous leukaemia group could be subdivided into phenotypic subsets. The importance of using panels of monoclonal antibodies in the diagnosis of acute leukaemias is discussed.