Asbestos is a commercial term for a group of fibrous minerals often associated with the development of pulmonary interstitial fibrosis (asbestosis), lung cancer, and malignant mesothelioma in occupationally exposed individuals. The pathogenicity of different forms of asbestos varies--long, thin amphibole fibers are most pathogenic, particularly in the induction of mesothelioma. Available data do not support the concept that low-level exposure to asbestos is a health hazard in buildings and schools. The concentration of asbestos fibers in air, type of asbestos, and size of fibers must be considered in evaluation of potential health risks.

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A B S T R A C T Evidence for the presence of peroxidative metabolism in rabbit alveolar macrophages (AM) has been obtained from the following observations: (a) catalase is present in high concentrations; (b) peroxidase activity could not be detected employing guaiacol as substrate; (c) the irreversible inhibition of AM catalase by aminotriazole served as a detection system for H202 and demonstrated increased intracellular H202 after phagocytosis; (d) formate oxidation, a marker of catalase-dependent peroxidations, occurs in resting AM and is increased by phagocytosis; (e) measurements of H202 accumulation in a dialysate of AM demonstrated twofold increase during phagocytosis; and (f) aminotriazole diminishes 02 utilization and '4CO2 production from labelled glucose and pyruvate. It is concluded that, while catalase-dependent H202 metabolism is not essential for particle entry, this pathway represents one of the metabolic pathways stimulated by particle entry in the AM. INTRODUCTIONThe alveolar macrophage (AM) plays an important role in pulmonary bacterial clearance by functioning as a phagocyte. While phagocytosis by the AM requires oxygen and stimulates both 02 consumption (Qo2) and 14CO2 production from labeled glucose (2), the relation of these metabolic pathways to H202 has not been de-