DNA repair following ultraviolet (UV)-induced DNA damage is decreased in some cancer-prone diseases. Cancer frequency in end-stage renal disease patients is higher than in the normal population. Therefore, DNA repair from UV-induced damage in lymphocytes was determined in 11 hemodialysis (HD) patients, 11 patients on continuous ambulatory peritoneal dialysis (CAPD), 10 patients with chronic renal failure (CRF) who had not yet been dialyzed and in 12 controls. UV irradiation at 254 nm was followed by 3H-thymidine incorporation in the presence of hydroxyurea. DNA repair synthesis in CAPD and CRF was significantly reduced to only 69 and 54% of the control, respectively, whereas the repair of HD patients was close to normal (86%, p = n.s.). The impaired ability to correct DNA damage may contribute to the increased cancer incidence in uremic patients.