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.