Ethanol 27.1 mmol/kg body weight, was administered intraperitoneally to rats in the weight classes 25, 50, 100, 150, 200 and 250 g. Controls were given saline, the total number of animals used being 120. Blood ethanol concentration and performance on the tiling-plane test was determined before and up to six hours after administration. Total ethanol elimination was low in the smallest weight classes, increasing during adolescence. The three smallest weight classes showed no impairment of performance after ethanol, while the 150-250 g classes were significantly impaired during the time of maximum blood ethanol concentration.