Salsolinol, a compound putatively formed following alcohol ingestion, differentially decreased the activity of lines of mice after 18 generations of genetic selection for alcohol sensitivity. Low doses of salsolinol produced significantly lower activity levels in the alcohol-sensitive long-sleep (LS) line than in the alcohol-insensitive short-sleep (SS) line. A hypnotic dose of salsolinol induced significantly longer sleeptimes in the LS line than in the SS line. Results are interpreted as supporting the hypothesis that salsolinol-like substances may mediate some of the effects of alcohol on the central nervous system.