Melatonin, NAS, 6-OHM, AFMK, and 5-MT enhance repair of DNA damage induced by UVB as indicated by comet assay. HEKn keratinocytes were treated with melatonin or its derivatives before and after UV-irradiation (200 mJ/cm2) for 3 h. Photographs show comets in UV-irradiated and non-irradiated keratinocytes. UV caused strand breaks in DNA which migrated in the electrophoretic field to form comet tails. Tail moment is used to measure DNA damage. Data are analysed using student t-test and labelled as * p<0.05, ** p<0.01.