Chronic administration of estrogen to male Syrian hamsters for 7.0 to 9.0 months induces a high frequency of estrogen-dependent renal cancers. We have proposed a sequential multistage scheme involving tubular cell damage, regenerative cell proliferation, aneuploidy, chromosomal imbalance, genetic instability, gene alteration, and amplification as essential steps for estrogen carcinogenesis in this model. A systematic study was undertaken to assess the expression of nuclear proto-oncogenes, c-myc, c-fos, and c-jun, and suppressor genes, p53 and WT-1, by Northern blot analysis to further support this scheme. Hamster kidney RNA, taken at monthly intervals (1.0 to 6.0 months) from diethylstilbestrol (DES)-treated castrated male hamsters and corresponding age-matched untreated controls was used in these studies, as well as primary estrogen-induced renal tumor RNA, for reference. Although no significant changes in the expression of these proto-oncogenes were detected in the first 4 months of estrogen treatment relative to age-matched controls, 2.1-kb c-myc expression was elevated 2.8- and 4.1-fold at 5.0 and 6.0 months, respectively. Moreover, the expression of 2.2-kb c-fos transcript rose 4.6- and 4.8-fold; and 3.2- and 2.7-kb c-jun expression increased 2.8- and 5.1-fold at these same respective estrogen treatment time intervals. Tumor suppressor gene expression, p53 and WT-1, was also evaluated in similar estrogen-exposed hamsters. Although no significant changes were found in hamster kidney p53 expression in the first 5.0 months of DES treatment, it rose 1.8-fold at 6.0 months of estrogen treatment and more than 2.0-fold in the primary renal tumor. In contrast, no detectable changes in WT-1 expression were found during the first 6.0 months of DES treatment. However, a dramatic 7.0-fold increase in WT-1 expression was observed in the primary renal tumor. It is evident that two WT-1 transcripts reside in the hamster kidney; a lower molecular weight transcript was found in the normal adult kidney, and a higher molecular weight 3.2-kb transcript was observed in the renal tumor, similar to that seen in the newborn mouse kidney. In summary, the estrogen-induced inappropriate gene expression, including p53, reported herein, is consistent with the view that the elevations seen in gene expression contribute to proliferative advantages of certain proximal tubular interstitial cells necessary for estrogen-driven tumor formation in the hamster.