Guinea pig bronchi sensitized to ovalbumin were set up in isolated tissue baths according to the method of Hooker and associates (1,2). In the presence of 10(-6)M atropine, pyrilamine, and indomethacin, concentrations of ovalbumin from 10(-9) to 10(-8) g per ml produced marked contraction of the bronchi. Generally, the antigen-induced contraction could be repeated every 45 to 60 min without tachyphylaxis. Ethanol (1.5 per cent), propanol (0.75 percent), butanol (0.25 per cent), and propylene glycol (1.5 per cent) decreased the contracile response to ovalbumin but either did not influence (ethanol and propylene glycol) or slightly reduced (propanol and butanol) responses of the bronchi to prostaglandin F2alpha. Trachea, bronchi, and parenchyma from sensitized guinea pigs were minced, washed, incubated in Krebs'-bicarbonate solution and challenged with 10(-6) and 10(-4) g per ml ovalbumin. Mediators released into the medium were assayed on unsensitized guinea pig ileum. All the alcohols suppressed mediator release. Circular dichroism demonstrated that the conformational integrity of ovalbumin was not altered by the concentrations of alcohols used in this study. These results show that antigen-induced mediator release is inhibited by alcohols and suggest caution when choosing a solvent for testing the effect of water insoluble anti-asthma compounds.