The establishment of Clusters of Differentiation for T- and B-lymphoid cells during International Workshops on Human Leukocyte Differentiation Antigens prompted the authors to evaluate the immunophenotypes in 160 cases of non-Hodgkin's lymphoma (NHL). In this group, 130 were of B-lymphocyte lineage (117 by monotypic immunoglobulin expression), and 30 of T-cell lineage. In the B-NHL series the expression of immunoglobulin isotypes, B-cell maturation/differentiation antigens of CD9, CD10, CD19-24, CD37, and CD38 (OKT10), HLA-DR and peanut agglutinin binding showed no significant relationship with histopathologic diagnosis as defined by the Kiel classification. Of the T-cell markers, CD5, CD6, and CD7 showed lineage promiscuity by their presence on some B-NHL. Conversely, the authors grouped the cases according to phenotypes (either CD antigens or immunoglobulin isotypes) which occur in distinct stages of (physiologic) B-cell maturation/differentiation. Eighty-six of the 130 cases could be fitted according to CD phenotype expression. This approach did not yield a significant relationship between phenotype and individual histopathologic categories either. The staging by CD phenotype and by immunoglobulin isotype yielded different results in this respect. Most B-NHL had an intermediate stage of B-cell maturation/differentiation. In the T-NHL series most cases showed a phenotype (CD1-CD8, CD38, TdT, and peanut agglutinin binding capacity) compatible with mature T-lymphocyte characteristics. The exceptions were lymphoblastic convoluted lymphomas, which exhibited an immature immunophenotype. It is concluded that NHL in distinct histopathologic categories are heterogeneous in immunologic phenotypes, and that the immunophenotype of lymphoma cells has no evident association with that of their presumed counterparts in physiologic cell maturation/differentiation.