The biotin-avidin immunoperoxidase assay was used to evaluate the expression of several prostate carcinoma-associated markers in formalin-fixed paraffin-embedded tissue sections of three human prostate nude mouse heterotransplant lines PC-82, PC-EW, and PC-EG. In addition to monoclonal antibodies to PSA and PAP, monoclonal antibodies to five other potentially useful markers for prostate carcinomas (TURP-27, Leu-7, 7E11-C5, PSP-19, and PD41) were tested. Tissues from two or more transplant passages were evaluated. The human prostate target antigens were found to be expressed by one or more of the three heterotransplant lines. The PC-82 and PC-EW lines were the most efficient in terms of expression of multiple prostate carcinoma-associated markers and percentage of tumor cells positive for a given prostate antigen. The staining pattern of each marker, in terms of staining intensity, number of tumor cells stained, and staining location, i.e., membrane, cytoplasmic, or ductal secretions, was similar to what has been observed in tissue sections from human prostate carcinomas. The lack of an appropriate model for evaluating the preclinical potential of these Mabs (especially TURP-27, PSP-19, and PD41) makes the findings of this study of considerable importance, and suggests that these human prostate xenografts may be useful models for exploring the diagnostic and therapeutic potential of these anti-prostate carcinoma monoclonal antibodies.