Ethanol (0.40 g/kg) was administered to 13 healthy men by intravenous (i.v.) infusion at a constant rate for 30 min. The concentrations of ethanol in arterial blood (ABAC), venous blood (VBAC), and end-expired breath (BrAC) were measured at 17 exactly timed intervals. Blood-ethanol was determined by headspace gas chromatography and breath-ethanol was measured with a quantitative infrared analyzer (DataMaster). BrAC was multiplied by 2300 to estimate the concentrations of alcohol in blood. During the infusion of ethanol, ABAC exceeded VBAC by about 10 mg/dL on the average and ABAC was also higher than BrAC × 2300 by about 4 mg/dL on average. When infusion of alcohol ended, ABAC, VBAC, and BrAC were 94.8 ± 2.06 (±SE), 84.7 ± 1.54, and 89.3 ± 2.10 mg/dL, respectively. The concentrations of alcohol in blood (ABAC and VBAC) and breath decreased abruptly after the administration of alcohol stopped and by 5 min postinfusion, the A-V differences in concentration of ethanol were small or negligible. The mean apparent half-life of the distribution plunge was 7 to 8 min, being about the same for ABAC, VBAC, and BrAC. The disappearance rate of ethanol was 15.5 ± 0.55 mg/dL/h (mean ± SE) for arterial blood, 15.2 ± 0.49 mg/dL/h for venous blood, and 16.3 ± 0.73 mg/230 L/h for breath; no significant differences were noted (p > 0.05). We conclude that A-V differences in the concentration of ethanol exist during the loading phase but are rapidly abolished when the administration of ethanol terminates. In the post-absorptive phase of ethanol kinetics, when alcohol has mixed with the total body water, VBAC exceeds ABAC by about 1–2 mg/100 mL on average.