Acetone-fixed frozen sections of reactive lymph node, spleen, three B cell lymphomas, and three T cell lymphomas were studied for the presence of Ia-like antigens and two T cell antigens. Detection of the binding of the hybridoma monoclonal antibodies to these antigens took advantage of the biotin-avidin interaction. The detection method employed a biotin conjugate of goat anti-mouse antibody and an avidin conjugate of horseradish peroxidase. B cell lymphoma cells stained for Ia. The cell lymphomas were shown to be heterogeneous for the expression of the two T cell antigens. these three antigens were generally not detectable after 10% formalin fixation of B-5 fixation. Detection of these antigens and the method employed should prove useful in the immunologic categorization of human lymphomas.