The concentrations of Platinum Group Elements (PGE) (Pt, Rh, Pd and Ir) in the atmosphere of urban areas have been progressively increased as a consequence of their release from the automotive catalytic converters and their adsorption in the particulate material. The PGEs catalytic activity is therefore extended also outside the vehicle converters. In the environment, PGEs come in contact with inorganic and organic structures, in particular with living organisms. Beside the photochemical smog (mainly ozone production/degradation), several redox reactions, involving free radicals and promoted by PGEs, can become responsible for interactions at the metabolic pathways level. The environmental monitoring confirms the increasing concentrations of ozone and of PGEs in urban air. To approach such a complex problem, in vitro experiments have been performed on enzyme kinetics and on antioxidants in living systems. Preliminary data on enzymatic systems (NADH) and on antioxidants (ascorbic acid) in the presence of some PGEs are reported. Copyright © 2007 Inderscience Enterprises Ltd.