Patients with vitiligo received 6-9 ultraviolet B treatments, 2 to 3 times weekly. Minimal erythema dose (MED) testing was done at baseline and after all treatments; the percent change in MED was analysed as a measure of photoadaptation. The percent decrease in cyclobutane pyrimidine dimers (CPDs) over 24 hours after a single exposure of 1 MED was analysed on vitiliginous and normal skin.