To the Editor: In reference to the interesting communication of Chilcote et al. (Aug. 1 issue)1 regarding the association of “lymphomatous ALL [acute lymphoblastic leukemia]” and abnormalities of the short arm of chromosome 9, I would like to point out the following: in their Discussion, the authors interpret the absence of surface-membrane immunoglobulin as suggesting that the leukemic cells are not of B-cell origin. Surface-membrane immunoglobulin appears relatively late in B-cell ontogeny. Commitment to B-cell differentiation can be indicated by the presence of HLA-DR-associated antigens, which are seen in T cells only upon activation. Other surface and cytoplasmic markers appear. © 1985, Massachusetts Medical Society. All rights reserved.