Previous methods to deplete in vivo concentrations of reduced glutathione (GSH) have not been able to lower tissue GSH levels for extended periods, have been toxic, and can alter the metabolism of xenobiotics. A possible alternative to lower in vivo concentrations of GSH may be the use of buthionine-S,R-sulfoximine (BSO) in the drinking water of laboratory animals to inhibit the biosynthesis of GSH. It has been previously reported that 20 mM BSO in the drinking water given to mice was able to lower GSH levels in a variety of tissues after 15 days. In order to more fully characterize the in vivo depletion of GSH in tissues by ingestion of BSO and determine if this method would be suitable in studies requiring depressed levels of GSH for extended periods, we added different amounts of this agent to the drinking water given to mice for various times up to 28 days. We found that ingested BSO at the highest concentration used in drinking water (30 mM) was able to maximally lower GSH concentrations in mouse lungs, lung lavage fluid, liver, kidneys, and blood to 59.0 +/- 3.6%, 35.0 +/- 5.1%, 44.3 +/- 1.5%, 69.5 +/- 3.9%, and 70.0 +/- 6.0% of control mice, respectively, for up to 28 days. These lowered concentrations of tissue GSH returned to control levels after mice were returned to untreated drinking water for 7 days. The potential toxicity of such treatments was also evaluated. Levels of alkaline phosphatase, lactate dehydrogenase, glucose-6-phosphate dehydrogenase, glutathione peroxidase, and glutathione reductase in lungs and lung lavage fluid, and total and differential cell counts from lung lavage fluid were not different between control and BSO-treated mice. This showed that BSO treatment did not produce indications of lung injury as measured by these biochemical parameters. Serum aspartyl transferase and gamma-glutamyl transpeptidase activities were unaffected by the BSO treatments, indicating normal liver functions. Lung and liver cytochrome P-450 concentrations were also not different between controls and BSO-treated animals. Thus, BSO in the drinking water of mice was able to effectively lower in vivo levels of GSH without eliciting acute toxic responses.