We immunophenotyped 128 patients with B-cell non-Hodgkin's lymphoma (B-NHL) of various histological subtypes using two-color flow cytometry (FCM), and found that lymphoma cells obtained from 31 patients (24.2%) coexpressed at least one of the following T-cell associated antigens (T-Ag); CD2 (2.3%), CD5 (18.0%) or CD7 (6.3%). Moreover, 3 patients expressed two kinds of T-Ag (CD2/CD5, CD2/CD7 or CD5/CD7) as reported by other investigators. Though we could not find coexpression of CD3, CD4 or CD8 antigen in any patients analyzed in our study, such T-Ag(+) B-NHL have also been reported in the literature. As clinical features, extranodular involvement and higher International Prognostic Index (high and high intermediate) seemed more frequent in T-Ag(+) B-NHL than T-Ag(-) B-NHL in our study. Such prognostic significance of T-Ag expression is also reported by other investigators especially in CD5(+) diffuse large B-cell lymphoma. In addition, two-color FCM for detecting such aberrant T-Ag expression in B-NHL is useful for monitoring the minimal residual disease in the subgroup with T-Ag(+) B-NHL.