Reactive oxygen and nitrogen oxide species and their inducing stress are involved in a variety of physiological and pathological phenomena in aerobes, including humans. For multistage carcinogenic processes, reactive oxygen and nitrogen oxide species-induced stress (RONOSS) serves as a major intrinsic factor and is involved in every step. This means that free radicals, RONOSS and their inducing downstream events may be targets for cancer prevention. It is therefore of importance to elucidate the mechanisms underlying the participation of RONOSS in carcinogenesis and to apply the obtained results for establishment of strategies to control cancer development. Despite the large body of accumulated knowledge due to worldwide efforts dealing with this research field, there still remain numerous uncertainties. In this mini-review, we introduce two examples of such efforts, one concerning a renal carcinogen KBrO3 and the other dealing with hepatocarcinogenesis caused by a choline-deficient, L-amino acid-defined diet, in order to give some idea about the current understanding of the roles of RONOSS in carcinogenesis.