Response to oxidative stress has been hitherto scarcely studied in the respiratory yeast Kluyveromyces lactis. The genes coding for reductases of glutathione and thioredoxin, KlGLR1 and KlTRR1, respectively, have been cloned and characterized in this work. H(2)O(2) treatment increased transcription and enzyme activity of KlTRR1 but not of KlGLR1, suggesting a different situation from that reported for the fermentative yeast Saccharomyces cerevisiae. A consensus for Yap1p binding is functional in the KlTRR1 promoter.