CD3 is expressed throughout the T-cell differentiation process. CD3 is a highly specific and sensitive T-cell lineage marker, making it ideal for the immunophenotypic analysis of lymphohaematopoietic malignancies. Notable exceptions include some of the more aggressive large T-cell lymphomas and CD30 (Ki-1) positive anaplastic large cell lymphomas, which may not express detectable antigen (1-3). CD3 [LN10] has demonstrated optimal staining when compared to other CD3 clones including PS1, F7.2.38 and SP7 (4). A monoclonal antibody to human CD3 is regarded as a reliable pan T-cell antibody used in the immunophenotyping of lymphomas in paraffin sections.