Immunocytochemical identification of human chorionic gonadotropin. Comparative study of diaminobenzidine and 3-amino, 9-ethylcarbazole, a nonhazardous chromogen.

An immunomicroscopic study evaluated 55 fixed, paraffin-embedded tissues from surgical and necropsy-accessioned material reflecting a variety of physiologic and pathologic disorders. The sensitive unlabeled (peroxidase-antiperoxidase) immunoperoxidase technique was used. Cytoplasmic human chorionic gonadotropin (CHCG) was readily identified in syncytial trophoblastic cells. The only tissue sections that did not demonstrate CHCG activity were primary and secondary testicular teratocarcinomas without choriocarcinoma components. When the technique was reevaluated for the non-hazardous chromogen 3-amino, 9-ethylcarbazole, excellent results were achieved with equivalent staining distribution and intensity. The unlabeled immunoperoxidase method for the identification of CHCG is a sensitive, reliable, confirmatory immunohistochemical stain. A relatively safe chromogen can be substituted for the benzidine derivatives in the procedure with equivalent results.