Intracerebroventricular (icv) administration of neurotensin produced a dose-dependent increase in ethanol sensitivity as measured by blood ethanol concentration at loss of righting reflex in SS/Ibg (SS) but not in LS/Ibg (LS) mice. Central administration of calcium also enhanced ethanol sensitivity of SS and to a lesser extent LS mice. Concurrent icv administration of calcium and neurotensin resulted in an additional enhancement of sensitivity to ethanol over that seen with either substance alone in both mouse lines. A dose-dependent increase in ethanol sensitivity was also produced in response to central administration of beta-endorphin in SS mice. No additional increase in sensitivity was noted following administration of beta-endorphin plus calcium. These results suggest a specific interaction of calcium and neurotensin may be involved in the mechanism through which ethanol elicits intoxication. The difference in response of LS and SS mice to neuropeptide and calcium-induced alterations in ethanol sensitivity may be related to the genetically selected differences to the acute narcotic actions of ethanol in these mice.