Forty-five young men were given an initial dose of ethanol calculated to achieve a blood alcohol concentration (BAC) of 100 mg of ethanol/100 ml of blood. Using breath analysis, the rates of ethanol clearance were calculated over a period of a few hours. When each individual reached a BAC level exactly one-half (about 50 mg%) that seen at his peak BAC, he was given a second dose of ethanol amounting to 45% of his initial dose, and the clearance rate was again determined. Estimates of absorption time, peak BAC, volume of distribution, clearance rate, and other metabolic parameters were made separately following each dose of ethanol. As intended, there was no significant difference between peak 1 and peak 2; however, there was a significant increase in clearance rate (beta 60) after dose 2. We term this phenomenon acute metabolic tolerance to ethanol ( AMTE ). When the sample was stratified by ethnicity, there was a trend for men of Oriental ancestry to clear the drug at a faster rate than was the case for men of Caucasian or Polynesian ancestry. The data also indicated that prior drinking history may have had an effect on clearance rate, though this differed by ethnicity. Two different methods for estimating volume of distribution (V) were used. The correlation between the separate estimates obtained was poor, and is probably an indication of the need for development of more accurate methods for estimating V.