Effects of carbon dioxide modified atmospheres on degradation of adenine nucleotides in chill-stored whitefish (Coregonus clupeaformis) and rainbow trout (Salmo gairdneri) were studied. K values were determined during storage up to 26 days. Results indicated CO2 atmospheres did not alter K values compared to those observed for aerobically held fish. However, both CO2 atmospheres and potassium sorbate-dipping of fillets caused decreases in hypoxanthine concentrations compared to untreated aerobically held samples.