Cell suspensions or frozen sections of lymph node biopsies from 32 patients with non-Hodgkin's lymphoma (NHL) were studied for sheep erythrocyte (E)-binding under three conditions (Estandard, EAET, Egravity), Fc and C receptors, immunoglobulin (Ig) heavy and light chain class and reactivity with heterologous antisera to T cells (T-LCL), HLA-D (Ia-like) and common acute lymphocytic leukemia (c-ALL) antigens. Selected B and T cell lymphomas were also tested for reactivity with the monoclonal antibodies OKT 3, OKT 4, OKT 6, OKT 8, OKT 11A, Leu-1, Leu-2a, Leu-3a, Leu-4 and Leu-7. There were 26 B and 6 T lymphomas. Most B lymphomas were mu+ (81%), kappa+ (77%) and 31% were mu+ delta+. One of the T lymphomas arose in a patient with antecedent follicular small-cleaved (B) cell lymphoma. The most accurate marker for characterizing the immunologic phenotype in NHL was the clonal excess of kappa+ or lambda+ cells. Neither Estandard, EAET, Egravity or T-LCL were consistently reliable as sole reagents in identifying T-cell lymphomas, their individual scores often being lower than those of monoclonal pan-T cell reagents. HLA-D (Ia-like) antigen was noted in 89% of B and 50% of T lymphomas. The corresponding values for c-ALL antigen were 12 and 33%, respectively. The comparative scores in T-lymphomas between OKT 4 and Leu-3a for "helper-inducer" (HE) cells and OKT 8 and Leu-2a for "suppressor-cytotoxic" (SU) cells were not uniformly consistent. Four T lymphomas had a mixed HE/SU cell phenotype, one was HE, and another SU. Anti-T reactivity was detected in the neoplastic follicles of six of seven follicular lymphomas. The percentage of anti-T reactive cells within positive neoplastic follicles was usually small (5-15%) and of the same order as that noted within reactive lymphoid follicles (5-30%). High numbers (50-100%) of cells from five small lymphocytic B, three diffuse small cleaved cell B and six T cell lymphomas were also positive with one or more anti-T reagents, suggesting the presence of cross-reactive antigens that make phenotyping of lymphomas with monoclonal antibodies problematic. Reactivity with the monoclonal antibody Leu-7 (HNK-1), a putative NK-specific reagent, was seen in one of five B and three of five T lymphomas.