To test the validity of a possible correlation of cytotoxicity, the authors attempted to evaluate asbestos (1332214) minerals with known fibrogenic potential and fiberglass, using a battery of in-vitro bioassays. The objective of this study was to assess the potential role of several asbestos fiber types in the generation of hydroxyl radicals from hydrogen-peroxide and to correlate in-vitro cytotoxicity, lipid peroxidation potential and in-vitro generation of oxygen radicals during phagocytosis. Chrysotile (12001295), amosite (12172735), and crocidolite (12001284) asbestos fibers, and Code-100 fiberglass were used. Tests conducted included electron spin resonance (ESR) measurements of radical generated from minerals in-vitro, cytotoxicity in sheep erythrocytes, rat alveolar macrophage enzyme studies, lipid peroxidation, and ESR measurements of oxygen radicals during phagocytosis by rat alveolar macrophages. The findings suggested that several mechanisms are likely to be involved in the generation of oxygen radicals during asbestos cell interactions. Bioavailability of iron on the surface of asbestos is a major factor in the production of oxygen radicals. The ability of asbestos to perpetuate the generation of oxygen free radicals as a result of cell death and recycling of fibers from repetitive phagocytosis may be a major factor. The authors also suggest that frustrated phagocytosis by several phagocytes commonly observed on long asbestos fibers may be a major source of oxygen free radicals.