Mice injected intraperitoneally with sulfolane (tetrahydrothiophene-1,1-dioxide) underwent a significant decrease in metabolic rate and body temperature at ambient temperatures of 20 and 30 degrees C but not 35 degrees C. If given the opportunity, mice treated with sulfolane preferentially sought a cool ambient temperature. When given an LD50 dose of sulfolane (1270 mg/kg), the percentage mortality varied directly with ambient temperature. For example, at 35 degrees C mortality was 75% whereas at 25 degrees C mortality was only 8%. By undergoing an autonomically and behaviorally mediated decrease in body temperature (i.e., regulated hypothermia), sulfolane-treated mice appear to enhance their chance of survival.