Pulmonary injury after acute H_2S inhalation was studied with bronchoalveolar lavage(BAL),ultracentrifuge,and optical and electron microscopy.The changes of the activities oflactate dehydrogenase,alkaline and acid phosphatase,and angiotension converting enzymes inBAL fluid were used as the indicator of cellular damages,those of leucocytic count and the indi-cator of inflammatory response,and those of the concentration of protein and Evans blue as theindicator of vascular permeability.In addition the effects of H_2S on lipid peroxidation,naturalantioxidative system and energy substances and the changes of phospholipid concentration inBAL fluid were also observed.The results were as follows:1.Inhalation of H_2S exerted a severe cytotoxic effect on the lung tissues resulting in dam-ages on various types of cells and a severe edematogenic effect on lung parenchyma.2.The development of pulmonary edema in H_2S intoxication resulted from a combination ofdifferent pathogenic factors.3.The biochemical changes and their recovery occurred earlier than the pathologicalchanges and their recovery.The efficacy of 6 categories of drugs including 25 medicaments against H_2S intoxication wasevaluated in mice,and 10 drugs were found to be prophylactically effective.The effects of vari-ous methemoglobin-forming agents and some other drugs were also studied in their treatment ofH_2S intoxication in rabbits and dogs.It was concluded that methemoglobin-forming agentscould be used as specific antidotes but could not provent or alleviate the lung damages due toH_2S inhalation unless they were administered in association with dexamethasone,vitamin E oranisodamine.A scheme of the medical treatment for H_2S intoxication was presented. Pulmonary injury after acute H_2S inhalation was studied with bronchoalveolar lavage (BAL), ultracentrifuge, and optical and electron microscopy. The changes of the activities of lactate dehydrogenase, alkaline and acid phosphatase, and angiotensin converting enzymes in BAL fluid were used as the indicator of cellular damage , those of leucocytic count and the indi-cator of inflammatory response, and those of the concentration of protein and Evans blue as theindicator of vascular permeability. addition the effects of H 2 S on lipid peroxidation, naturalantioxidative system and energy substances and the changes of phospholipid concentration in BAL fluid was also observed. results were as follows: 1. Inhalation of H 2 S exerted a severe cytotoxic effect on the lung tissues resulting in dam-ages on various types of cells and a severe edematogenic effect on lung parenchyma. 2. the development of pulmonary edema in H_2S intoxication resulted from a combination of differential pathogenic factors. The bioc hemical changes and their recovery occurred earlier than the pathologicalchanges and their recovery. The efficacy of 6 categories of drugs including 25 medicaments against H_2S intoxication wasevaluated in mice, and 10 drugs were found to be prophylactically effective.The effects of vari-ous methemoglobin-forming agents and some other drugs were also studied in their treatment of H_2S intoxication in rabbits and dogs. It was therefore that methemoglobin-forming agents that used be specific antidotes but could not provent or alleviate the lung damages due to H_2S inhalation unless they were administered in association with dexamethasone, vitamin E oranisodamine. A scheme of the medical treatment for H_2S intoxication was presented.