Addition of hydrogen peroxide, menadione, or plumbagin to growing cultures of the fission yeast Schizosaccharomyces pombe increased trehalase activity. The effect was inhibited only slightly in the presence of cycloheximide, indicating that the stimulation of trehalase triggered by oxidative stress is mostly due to posttranscriptional activation. Northern blot analysis of trehalase mRNA level revealed that oxidative stress also induces a moderate rise in transcription of trehalase. Mutants disrupted in genes encoding elements of the mitogen-activated protein kinase (MAPK) cascade showed a reduced increase in trehalase activity upon oxidative challenge, which was coincident with a block in transcription of trehalase. Taken together, the results support the idea that the enhancement of trehalase by oxidative stress is due to enzyme activation (via the Pka1/Sck1 phosphorylation pathway) and induction of trehalase mRNA (via the MAPK signaling pathway). In spite of the trehalase increase, a net accumulation of trehalose was noticed during the oxidative stress.