A case of serious intoxication with CS tear gas (o-chlorobenzylidene-malononitrile) is reported in a previously healthy male subject of 43 years involving pulmonary edema complicated by pneumonia, signs of heart failure and evidence of hepatocellular damage. Comparison with animal and human exposures supports the etiologic and pathogenetic role of CS tear gas in the present case. The pulmonary edema may have been the consequence of unusual conditions of exposure and/or increased individual susceptibility. The question of the "safety" of CS tear gas is discussed.