The Ca 2+ -dependent response to oxidative stress caused by H2O2 ortert-butylhydroperoxide (tBOOH) was investigated inSaccharomyces cerevisiae cells expressing transgenic cytosolic aequorin, a Ca 2+ -dependent photopro-tein. Both H2O2 and tBOOH induced an immediate and short-duration cytosolic Ca 2+ increase that depended on the concentration of the stres-sors.