Disulfiram (Antabuse), a drug used in alcohol aversion therapy, has been demonstrated to protect various species against hyperbaric O2 toxicity. In contrast, we have found that disulfiram accelerates the onset of pulmonary edema and death of rats exposed to normobaric 95 to 97% O2. When rats were given 200 mg of disulfiram per kg b.wt., 100% of the rats died at 24 to 48 hr of O2 exposure whereas only 5% of the rats died when exposed to O2 without disulfiram. This effect was not seen with an equal dose of diethyldithiocarbamate, the reduced monomer of disulfiram. The toxic effect was not due to an inhibition of superoxide dismutase, nor did disulfiram significantly affect the level of glutathione or change the reduced to oxidized glutathione ratio in the lung. Concurrent administration of 200 mg per kg b.wt. of ascorbate, vitamin E or reduced glutathione or 100 mg/kg of catalase did not affect the toxic response.