Arterial and venous blood alcohol concentration (BAC)-time courses were completely defined in the peripheral circulations, both during and after the constant rate infusions of ethanol via the cephalic vein or hepatic artery in the dog. These BAC data were characterized by the following trends. (1) A much faster rise in the blood alcohol curve, as well as a higher peak BAC was found using the shorter infusion time. (2) During infusion, the alcohol concentration was higher in arterial or arterialized blood than venous blood when infusion was via the cephalic vein. (3) Peak BAC was higher in the femoral artery than the femoral vein whether infusion was via the cephalic vein or hepatic artery. (4) Peak BAC was higher in the hepatic artery or portal vein than the hepatic vein when infusion was via the cephalic vein. When administration was directly into the liver, the peak BAC in the hepatic vein was higher than the portal vein. (5) After infusion ceased, there was an arterial-venous inversion; peripheral arterial ethanol concentrations were significantly less (p less than 0.001) than corresponding venous concentrations; with cephalic vein administration, a hepatic vein-portal crossover was observed, the reverse being true when ethanol was administered via the hepatic artery. In either case, the BAC was observed to be higher in the hepatic artery than the portal vein or hepatic vein throughout the sampling period. (6) BAC was observed to be higher for the same sampling times at the respective sites when ethanol was administered directly into the liver. While the methodology in this study is prohibitive for human experimentation, correlations may be extended to man. The elaboration of the arterial-venous concentration differences for ethanol should prove beneficial in revealing the relationships among the doses of alcohol, the circulating blood ethanol concentrations, and physiological and psychomotor test parameters in man.