Hydrogen sulfide poisoning is frequently encountered in the workplace. Two workers lost their consciousness in an underground tank at a factory producing paper. The tank contained liquid mixture of used paper, sodium oxygenate chloride(NaOC1), and sodium thiosulfate pentahydrate(NaSO3 5H90). A worker(worker A; 36-year-old man) entered tank to remove sludge. When worker A lost his consciousness, worker B entered the tank to rescue worker A, however he lost consciousness inside the tank. We discuss in detail the clinical features of this condition. Hydrogen sulfide poisonings have occurred in industries involving petroleum refining, the manufacture of heavy water, tanning of hides, vulcanization of rubber, and the manufacture of rayon. And it is necessary to stress the health education for workers and managers in these industries.