Previous reports of the impact of ethanol on murine aggression have produced inconsistent findings; some workers have found that low doses of ethanol increase aggression whereas others have reported either no effect or a suppression. The present study examined one variable that may help to account for these inconsistencies, namely the level of blood alcohol at various times after administration. Acute doses of 0.5, 1, 2 g/kg ethanol all potently suppressed fighting in mice. However, there was no simple relationship between blood alcohol levels and fighting. It appeared that the level of blood alcohol, whether these levels were falling and the time since alcohol was cleared from the blood were all factors that influenced the drugs anti-aggressive influence.