Paraffin sections of 133 cases of non-Hodgkin's lymphoma (69 B-cell type and 64 T-cell type) were stained in a labeled streptavidin biotin immunoperoxidase technique with a panel of antibodies that recognized T-lymphocyte associated antigens. This study was done to determine the sensitivity and specificity of these reagents for phenotyping T-cell lymphomas. UCHL-1, polyclonal anti-CD3, Leu-22, and OPD4 stained 78%, 72%, 91%, and 69% of the cases of T-cell lymphomas, respectively. The phenotype of L-26 negative and CD3 or UCHL-1 positive accurately predicted T-cell phenotype in 95% (60 of 63) of the T-cell lymphomas and was not seen in any of the cases of B-cell lymphoma. Although Leu-22 was the most sensitive T-cell-associated marker in this series, its lack of specificity for T-lymphocytes limited its usefulness as part of a routine panel designed to distinguish between T-cell and B-cell lymphomas. In conjunction with other reports, this study supports the use of the T-cell markers CD3 and UCHL-1 in combination with the B-cell-associated marker L-26 to phenotype most efficiently non-Hodgkin's lymphomas in paraffin sections.