Exposure of rats to 20 ppm CS2 (the current MAC in various countries) for 8 h was followed by i.p. administration of 2 g/kg ethanol (blood level: 3-1‰) and another up to 4-h exposure to the same concentration of CS2. During the second exposure the acetaldehyde concentration increased significantly, the rise representing one third of the control values. Inhalation of 400 ppm CS2 for the same period, or 8-h exposures at 400 ppm CS2 on 5 consecutive days produced only a slight additional increase in acetaldehyde. The increased appearance of acetaldehyde in blood is considered to be due to inhibition of aldehyde dehydrogenase by CS2. This conclusion was derived from the significant lag in the clearance rate of acetaldehyde given i.v. (1 mmol/kg) after exposure at 400 ppm CS2/8 h, involving an increase of the excretion half-life of acetaldehyde (1 min, 45 s in the controls) to 2 min, 24 s. The finding thus obtained could be reproduced in man (adult males). At a blood alcohol concentration of approximately 0.75‰, maintained at this level for 8 h, the blood acetaldehyde concentration was found to be approximately 6 × 10−3‰; it rose significantly by about 50% during simultaneous 8-h exposure of the test subjects to a nonfluctuating, analytically defined concentration of 20 ppm CS2. When increasing the dose Of CS2 to 40 ppm and 80 ppm for 8 h, only a slight additional increase was noted. Administration of ethanol (ca. 0./5‰) for 8 h, instituted at 16 h after 8-h inhalation of 20 ppm CS2, produced a rise in blood acetaldehyde to slightly more than twice the control value. An approximately identical quantitative effect was observed after exposure to 20 ppm on 5 consecutive days at the same time of the day (8.00 a.m. - 4.00 p.m.). Under the conditions employed, there was no evidence of any subjective or objective signs of alcohol intolerance in terms of an “antabuse syndrome” in the experiments. Inhalation of CS2 vapor failed to exert a significant effect on the pharmacokinetic behavior of ethanol in with a blood alcohol content up to 0.8%., contact with CS2 is not likely to give rise to a CS2-alcohol reaction, provided the concentrations of CS2 encountered in the work environment are within the range of the MAC.