The article reports a case of acute T-cell leukemia (T-ALL) with the unusual CD3+, WT31 phenotype. On surface marker analysis, the blast cells were found to be CD7+, CD2-, CD5-, CD1-, CD4-, CD8-, CD3+ and negative for B-lymphoid and myeloid lineage. The cells had both TCR beta and TCR gamma gene rearrangement but had negative results with the monoclonal antibody WT31, which reacts with a framework epitope on the T alpha/beta heterodimer (Ti) of the conventional T-cell receptor (TCR). This suggests an association of the CD3 molecular complex with a different polypeptide (the alternate TCR gamma). In two similar reported cases of T-ALL (WT31-, CD3+, CD4-, CD8-), the CD3 molecular complex was found to be associated with a product of the T gamma gene.