Glutathione (GSH) is an abundant and ubiquitous low-molecular-mass thiol with proposed roles in many cellular processes including amino acid transport, synthesis of proteins and nucleic acids, modulation of enzyme activity and metabolism of xenobiotics, carcinogens and reactive oxygen species. This review describes recent findings in the lower eukaryote Saccharomyces cerevisiae that are leading to a better understanding of the role of this peptide in eukaryotic cell metabolism. In particular, two gene products involved in maintaining the levels of reduced GSH have been studied; namely, GSH1 encoding γ-glutamylcysteine synthetase, the first step in the biosynthesis of GSH, and glutathione reductase, which recycles glutathione to its reduced form. These studies indicate that GSH is an essential metabolite in yeast, and that it is required for protection against oxidative stress produced by mitochondrial metabolism and exogenous reactive oxygen species. These findings are discussed in the light of analogous observations made in higher eukaryotes.