Recent research findings suggest that the patterning of familial alcoholism may critically determine ethanol sensitivity and severity of alcohol-related problems in the offspring. The present study examined the effects of familial alcoholism density on psychophysiological responses to ethanol administration in college males. Subjects with a positive family history of alcoholism were classified into affected biological father only (LD-FHP) versus both father and at least one second-degree affected relative (HD-FHP), and were compared to family history negative (FHN) subjects. Subjects received 1 g/kg ethanol or placebo in a double-blind procedure. A battery of subjective, physiological and psychomotor measures were collected once prior to and four times following drink administration. HD-FHP subjects showed significantly greater subjective effects, body sway and skin conductance after alcohol ingestion than either FHN or LD-FHP subjects; in contrast, there was no difference on any measure for LD-FHP versus FHN subjects. Our findings of increased ethanol sensitivity as a function of familial density of alcoholism strongly suggest the importance of carefully defining family history characteristics in all studies examining potential markers or risk factors for alcoholism.