To understand the molecular mechanism of carcinogenesis in androgen-dependent tumors, we have searched for new markers which are associated with this process. In normal rat prostate and seminal vesicle, sulfated glycoprotein 2 (SGP-2) messenger RNA is barely detectable. However, we have found high levels of SGP-2 expression in the epithelial component of carcinomas of the prostate and seminal vesicle after initiation with iV-nitroso-./V-methylurea and promotion with testosterone propionate. We have also observed induction of SGP-2 expression in epithelial cells at early stages in carcinogenesis when cytologically malignant cells first begin to appear. SGP-2 has been reported previously to be associated with a variety of models of programmed cell death (apoptosis), including the prostate following castration. Our present findings provide a novel marker for carcinogenesis in the rat prostate and seminal vesicle. © 1993, American Association for Cancer Research. All rights reserved.