The interaction between isolation and the response to ethanol was investigated with a social behavior test and a loss of righting reflex paradigm. The time a pair of mice spent in active social interaction, aggressive behavior, and avoidance-irritability showed an isolation-related increase, while locomotor activity was not affected by 0-10 days of isolation. Ethanol (0.8 g/kg) reduced the social interaction time in mice isolated for 10 days and 2.0 g/kg ethanol reduced it in all groups. Ethanol induced a locomotor stimulatory effect both in group-housed and isolated animals. An aggression-inducing effect of 0.8 g/kg ethanol was observed only in mice isolated for 5 days, while mice isolated for 10 days reduced their aggressive behavior after this dose of ethanol. The loss of righting reflex after 3.5 g/kg ethanol did not appear to vary with isolation. The results suggest that isolation alters some effects of ethanol qualitatively (e.g., its effects on aggressive behavior) but leaves other effects (e.g., its locomotor stimulant and hypnotic effects) unchanged.