DNA damage in the form of cyclobutane pyrimidine dimers(CPDs) and (6-4) photoproducts(6-4PPs) induced by UV-B radiation in Arabidopsis thaliana at different temperatures was investigated using ELISA with specific monoclonal antibodies. CPDs and 64PPs increased during 3 h UV-B exposure, but further exposure led to decreases. Contrary to the commonly accepted view that DNA damage induced by UV-B radiation is temperature-independent because of its photochemical nature, we found UV-B-induction of CPDs and 64PPs in Arabidopsis to be slower at a low than at a high temperature. Photorepair of CPDs at 24degreesC was much faster than that at 0degreesC and 12degreesC with 50% CPDs removal during 1 h exposure to white light. Photorepair of 6-4PPs at 12degreesC was very slow as compared with that at 24degreesC and almost no removal of 6-4PPs was detected after 4 h exposure to white light at 0degreesC. There was evidence to suggest that temperature-dependent DNA damage and photorepair could have important ecological implications.