A 47-year-old man had an episode of severe respiratory failure after acute intoxication with arsenic. Features of the initial clinical presentation included nausea, vomiting, and diarrhea, acute psychosis, diffuse skin rash, and marked pancytopenia. A peripheral neuropathy then developed which resulted in severe weakness of all muscles of the limbs, the shoulder and pelvic girdles, and the trunk. The neuropathy continued to progress despite treatment with dimercaprol (BAL in oil). Five weeks after the initial exposure, the patient was no longer able to maintain adequate ventilation and required mechanical ventilatory support. Improvement in the patient's neuromuscular status permitted successful weaning from the ventilator after one month of mechanical ventilation. Long-term follow-up revealed no further respiratory difficulty and slow improvement in the strength of the peripheral muscles.