Both the polyclonal anti-c-erbB-2 peptide antiserum pAB 60 and the monoclonal anti-c-erbB-2 protein antibody mAB-1 detect the c-erbB-2 protein in human breast adenocarcinomas. We investigated c-erbB-2 expression in adult human benign hyperplastic and neoplastic prostates, using the avidin-biotin complex immunoperoxidase method. Formalin-fixed, paraffin-embedded specimens of benign hyperplastic prostate (13), prostatic adenocarcinoma (22), and prostatic adenocarcinoma lymph node metastases (two) were tested with pAB 60. Ten formalin-fixed, paraffin-embedded specimens of prostate adenocarcinoma, 11 frozen sections of benign hyperplastic specimens, and eight frozen sections of prostate adenocarcinoma were tested with mAB-1. Our results demonstrated consistent detection of c-erbB-2 immunohistochemically in frozen sections of both benign and malignant prostate. Preincubation of pAB 60 with the immunizing peptide blocked subsequent reactivity with prostatic tumor tissue, indicating specificity. However, fixation and processing protocols significantly affected the reactivity of the antigenic determinants detected by these antibodies, as mAB-1 was nonreactive with formalin-fixed, paraffin-embedded prostatic tissues. Differential reactivity of pAB 60 with malignant rather than benign glands was maximized by exposure of the specimen to the antibody at 4 degrees C rather than 22 degrees C. The most frequently observed staining pattern with both antibodies was cytoplasmic. However, mAB-1 produced distinctly membranous staining in two frozen specimens of benign hyperplasia and one specimen of prostate cancer.