The level of mRNA expression and DNA structure of c-H-ras were examined in a transitional cell carcinoma (TCC) induced in C3H/He mice and Fisher rats by N-(4,5-nitro-2-furylthiazolyl)formamide (FANFT) and carried as serially transplanted tumors. Neither amplification nor gross rearrangements were detected by Southern analysis in the FANFT tumor. Increased expression of c-H-ras was detected by Northern and in situ hybridization in both the FANFT-induced mouse and rat TCC, as compared to normal urothelium. No expression of six other cellular oncogenes was detected in the tumor. It appears that the increase in H-ras expression in the FANFT tumor is specific to this oncogene and that increased expression of the H-ras gene may play a role in bladder carcinogenesis.