Adrenal androgens are discussed as a reason for tumor progression after androgen ablation therapy. Because of the difference in the secretion of androgens by the adrenals of humans and rats, there is no reliable tumor model to study the role of adrenal androgens in tumor progression. Therefore, the main adrenal androgens were administered to rats in order to mimic human endocrine conditions. Application of dehydroepiandrosteron-sulfate (DHEA-S) alone or a mixture of androstendione (A), 11 beta-hydroxyandrostendione (OHA), dehydroepiandrosterone (DHEA), and its sulfate (DHEA-S) to castrated rats caused only a slight increase of prostate and seminal vesicle weight. Contrary to these findings, growth of the R3327 prostatic carcinoma in castrated rats was greatly stimulated by these adrenal androgens up to the level of the intact control. Thus, in spite of androgen ablation, tumor progression could be induced by exogenous adrenal androgens.