The hypothesis that the central nervous system (CNS) of aged rats is more sensitive to acute ethanol effects was examined by measuring ethanol elimination rates, and the hypothermic and hypnotic responses to ethanol in four age groups (3, 12, 21, and 30 months) of Fischer 344 rats. Following a 2.5 g/kg intraperitoneal dose of ethanol, rectal temperature and blood ethanol concentration (BEC) were measured at regular intervals for 8 hr. The 30-month group's hypothermic response to ethanol was equivalent to the 3-month group's despite lower peak BEC. Response to a hypnotic dose (3.0 g/kg) of ethanol was evaluated by measuring the time for regain of righting reflex (RORR) and the BEC at RORR. The 3-month group slept for a shorter time, and awoke at a higher BEC, than the 12- or 21-month groups. The response of the 30-month group was more complex. Although this group had the lowest BEC at RORR, their sleep time was equivalent to the 3-month group. The shortened sleep time of the 30-month group is consistent with the observation of significantly lower peak BEC and higher metabolic rate (calculated from Widmark r values) in this group. Thus, aged rats of the Fischer 344 strain may be more sensitive to acute ethanol, but these CNS effects may be partially offset by enhanced ethanol disposition at older ages.