CD2 is one of the earliest T-cell lineage restricted antigens to appear during T-cell differentiation and only rare CD2+ cells can be found in the bone marrow. Anti-CD2 is a pan-T-cell antigen marker. Anti-CD2 is therefore useful for the identification of virtually all normal T-lymphocytes. It is also very useful in the assessment of lymphoid malignancies as it is expressed in the majority of precursor and mature T-cell lymphomas and leukemias. As with other pan-T-cell antigens, CD2 may be aberrantly deleted in some neoplastic T-cell populations, especially peripheral T-cell lymphomas. When combined with anti-CD25, anti-CD2 may assist in the identification of systemic mastocytosis and mastocytic leukemia.^1-4