The relationship between environmental temperature, body temperature and ethanol depression was investigated in male C57BL/6J mice. Animals were injected with ethanol (3.6 g/kg) or saline and placed in an experimental or normal room temperature (control) environment. Environmental temperatures from 12-37.degree. C significantly influenced rectal temperature, sleep-time and wake-up brain ethanol concentrations. Rectal temperatures of ethanol-treated animals ranged from 1.5.degree. C greater to 11.3.degree. C lower than their matched saline controls, supporting indications that ethanol impaired normal thermoregulation. Sleep-time decreased up to 43% and wake-up brain ethanol concentrations increased as rectal temperature decreased from .apprx. 38-32.degree. C. More severe hypothermia after ethanol (rectal temperature < 29.degree. C) increased sleep-time and decreased wake-up brain ethanol concentrations. Sleep-time and brain sensitivity to ethanol varied with rectal temperature in accordance with predictions based on membrane expansion and partition theories of anesthesia and the anticipated anesthetic-like actions of severe hypothermia.