The authors used an immunoperoxidase technique for the detection of immunoglobulins in frozen sections of 14 nodular lymphomas and ten reactive lymph nodes. Staining with antisera to the various immunoglobulin heavy and light chains permitted characterization and localization of neoplastic and non-neoplastic lymphoid cells in tissue sections. This technique is useful in the differential diagnosis of nodular lymphoma from follicular lymphoid hyperplasia. Non-neoplastic follicle mantle zones were found in six cases, providing additional evidence for the histogenic relationship between nodular lymphomas and lymphoid follicles. Hum Pathol 13:610-617, 1982.