Abstract: A total of 286 H(2)O(2)-sensitive Saccharomyces cerevisiae deletion mutants were screened to identify genes involved in cellular adaptation to H(2)O(2) stress. YAP1, SKN7, GAL11, RPE1, TKL1, IDP1, SLA1, and PET8 were important for adaptation to H(2)O(2). The mutants were divisible into two groups based on their responses to a brief acute dose of H(2)O(2) and to chronic exposure to H(2)O(2). Transcription factors Yap1p, Skn7p, and Gal11p were important for both acute and chronic responses to H(2)O(2). Yap1p and Skn7p were acting in concert for adaptation, which indicates that upregulation of antioxidant functions rather than generation of NADPH or glutathione is important for adaptation. Deletion of GPX3 and YBP1 involved in sensing H(2)O(2) and activating Yap1p affected adaptation but to a lesser extent than YAP1 deletion. NADPH generation was also required for adaptation. RPE1, TKL1, or IDP1 deletants affected in NADPH production were chronically sensitive to H(2)O(2) but resistant to an acute dose, and other mutants affected in NADPH generation tested were similarly affected in adaptation. These mutants overproduced reduced glutathione (GSH) but maintained normal cellular redox homeostasis. This overproduction of GSH was not regulated at transcription of the gene encoding gamma-glutamylcysteine synthetase.