The presence of pharmaceutically active compounds (PhACs) in aquatic systems is an emerging environmental issue and poses a potential threat to ecosystems and human health. Unfortunately, current water treatment techniques do not efficiently remove all of the PhACs, which results in the occurrence of such compounds in surface and ground waters. Advanced oxidation/reduction processes (AO/RPs) which utilize free radical reactions to directly degrade chemical contaminants are alternatives to traditional water treatment methods. This study reports the absolute bimolecular reaction rate constants for three pharmaceutical compounds (fibrates), clofibric acid, bezafibrate, and gemfibrozil, with the hydroxyl radical (*OH) and hydrated electron (e(-)(aq)). The bimolecular reaction rate constants for *OH were (6.98 +/- 0.12) x 10(9), (8.00 +/- 0.22) x 10(9), and (10.0 +/- 0.6) x 10(9), and for e(-)(aq) were (6.59 +/- 0.43) x 10(8), (112 +/- 3) x 10(8), and (6.26 +/- 0.58) x 10(8), for clofibric acid, bezafibrate, and gemfibrozil, respectively. Transient spectra were obtained for the intermediate radicals produced by the hydroxyl radical reactions. In addition, preliminary degradation mechanisms and major products were elucidated using (137)Cs gamma-irradiation and LC-MS. These data are required for evaluating the potential use of AO/RPs for the destruction of these compounds in treating water for various purposes.