Sulphydryl groups (-SH) play a remarkably broad range of roles in the cell, and the redox status of cysteine residues can affect both the structure and the function of numerous enzymes, receptors and transcription factors. The intracellular milieu is usually a reducing environment as a result of high concentrations of the low-molecular-weight thiol glutathione (GSH). However, reactive oxygen species (ROS), which are the products of normal aerobic metabolism, as well as naturally occurring free radical-generating compounds, can alter this redox balance. A number of cellular factors have been implicated in the regulation of redox homeostasis, including the glutathione/glutaredoxin and thioredoxin systems. Glutaredoxins and thioredoxins are ubiquitous small heat-stable oxidoreductases that have proposed functions in many cellular processes, including deoxyribonucleotide synthesis, repair of oxidatively damaged proteins, protein folding and sulphur metabolism. This review describes recent findings in the lower eukaryote Saccharomyces cerevisiae that are leading to a better understanding of their role in redox homeostasis in eukaryotic cell metabolism.