Higher plants express genes encoding peroxiredoxins of the two-cysteine type. This is concluded from the isolation of cDNAs from spinach (Spinacia oleracea) and barley (Hordeum vulgare cv. Gerbel) which are homologous to animal, fungal, and bacterial two-cysteine peroxiredoxins. Northern blot analysis indicated the presence of at least one corresponding gene in all angiosperms analyzed suggesting thatbas1 is a member of an ubiquitous gene family encoding a protein of fundamental importance in oxidative stress defense also in plants. In barley, expression increased upon application of methyl viologen but was not affected by ozone. mRNA levels increased during deetiolation in the light. Maximal abundance ofbas1 transcripts was observed in young developing shoot segments where cell division and elongation take place. Expression was insignificant in roots. The amount of bas1 protein was high in the leaf blade, particularly in etiolated plants, and did not respond to oxidative stress. bas1 protein was not detected in roots. From our data, we suggest that bas1 is an antioxidant enzyme particularly important in the developing shoot and photosynthesizing leaf.