To understand chemical characteristics of the asbestos minerals which might contribute to tissue damage, the catalytic properties of three different varieties were studied. Using spin trapping techniques it was determined that crocidolite, chrysotile, and amosite asbestos were all able to catalyze the generation of toxic hydroxyl radicals from a normal byproduct of tissue metabolism, hydrogen peroxide. The iron chelator desferroxamine inhibits this reaction, indicating a major role for iron in the catalytic process, and suggesting a possible mechanism by which asbestos toxicity might be reduced.