The potency of conventional inhaled anesthetics increases with maturation: the 50% effective dose (minimum alveolar anesthetic concentration [MAC]) for conventional inhaled anesthetics in the neonatal rat or human exceeds MAC in the young adult. This increase also applies to ethanol in rats tested using MAC as the measure of anesthesia. However, the converse appears to be true for studies in mice assessed with the righting reflex; that is, adult mice are six times more resistant than neonates to the effects of ethanol. These disparate findings imply that maturation in rats and mice may produce opposing changes in the quantity or sensitivity of one or more receptors that mediate the actions of anesthetics that lead to the anesthetic state. Such a finding would be important for two reasons. First, both rodents are widely used in studies of anesthetic effects, and, thus, a species-dependent divergence in anesthetic effects has immediate experimental implications. Second, confirmation of such a species difference would supply an opportunity to test which receptors might be crucial to anesthetic mechanisms. Accordingly, we investigated whether maturation decreased ethanol potency in mice, using MAC as the measure of anesthesia. Applying standard techniques, we tested MAC for ethanol in 15 CF-1 mice aged 10 days (6-8.5 g) and in 13 mice aged 77-84 days (34-39 g). MAC decreased with maturation, and the decrease was indistinguishable from that found in our previous studies of rats.