[en] Enhanced cell killing due to combined exposure to sunlight-like near-UV light (Westinghouse Sun Lamps, FS20) and X-rays, indicative of damage interaction was observed at all stages of the cell cycle. The greatest interaction was observed in the middle of the DNA synthetic phase. At equal survival, 'sunlight' damage was only partly additive to X-ray damage, and vice versa, whereas in earlier studies it was found that far-UV light (254 nm) produced damage completely additive to X-ray damage. Loss of damage interaction between radiation was more rapid after a first dose of X-rays than after a first dose of 'sunlight'. (author)