The psychological (expectancy) and physiological (dosage) effects of alcohol on aggressive and assertive behavior were investigated. The expectancy manipulation was accomplished by informing subjects that the beer they were to receive was either half as strong or twice as strong as commercially available beer. The dosage manipulation involved administering "blind" subjects either 0.0 (placebo), 0.5, or 1.0 ml of 95% pure ethanol per kilogram body weight. Male, social drinkers (N=54) were administered self-report and behavioral measures of aggressiveness and assertiveness following alcohol consumption. Analysis of the results indicated that both psychological and physiological effects of alcohol influenced aggression. A moderate dosage of alcohol increased self-report aggression scores, whereas a high dosage of alcohol increased scores on a behavioral measure of aggression. Additionally, subjects expecting a beer twice as strong as commercially available beer yielded higher aggressiveness scores than subjects expecting beer half as potent. Neither dosage expectancy nor actual dosage was found to influence assertiveness. (Author)