Four commercially available monoclonal antibodies, MB1, MB2, LN1 and LN2, were studied to determine their sensitivity and specificity for the diagnosis of B-cell lymphomas when used on formalin-fixed paraffin-embedded tissues. In addition to 125 cases of immunologically characterized non-Hodgkin's lymphoma, a range of normal tissues, reactive lymphoid proliferations, Hodgkin's disease and granulocytic sarcomas were also studied. MB1 was found to give positive results in 53.6% of B-cell lymphomas, but the staining was sometimes weak and patchy; there was also cross-reaction with 1.8% of T-cell lymphomas. MB2 reacted with 88.4% of B-cell lymphomas and the reaction was often strong and diffuse, but it showed cross-reaction with 18.2% of T-cell lymphomas. LN1 and LN2 gave positive staining of 44.9 and 46.4% of B-cell lymphomas respectively, and the results appeared to be inferior to that obtained in B5-fixed tissues; staining was sometimes weak and focal, and they also gave false-positive results in a few cases of T-cell lymphoma. This study shows that MB1, LN1 and LN2 are fairly but not entirely specific for B-cells in the non-Hodgkin's lymphomas, but are not very sensitive when applied to formalin-fixed tissues. MB2 shows a high sensitivity but only moderate specificity. Therefore, when these antibodies are used to determine the immunophenotype of malignant lymphomas, the B-cell nature can be predicted with great confidence only when two, preferably three or more, of the antibodies give positive results. The potential applications of these antibodies are discussed.