Environmental lung injury may take the form of acute tracheobronchitis, asthma, pulmonary edema, chronic bronchitis, emphysema, allergic pneumonitis, fibrosing alveolitis, pleurisy, and neoplastic disease. Environmental factors eliciting these responses include irritant gases and fumes, oxidants, organic allergens, inorganic dust, bacterial enzymes, and high partial pressures of oxygen. The basic pulmonary reactions to these toxic agents--bronchoconstriction, vasoconstriction, increased vascular permeability, inflammation, carcinogenesis--may be mediated, aggravated, or modulated by biologically active substances. These humoral agents include biogenic amines (e.g. histamine): peptides (e.g., bradykinin, vasoactive intestinal peptide, and spasmogenic lung peptide); enzymes (e.g., proteases, superoxide dismutase, and mixed function oxidases); and acidic lipids (e.g., prostaglandins, prostaglandin endoperoxides, and thromboxanes).