A multicentre randomised controlled trial of xenon-arc photocoagulation for diabetic maculopathy is reported. This interim account reports the visual-acuity results of those who were followed up for up to three years. 76 patients were seen after one year, 44 after two years, and 25 after three years. Initially each patient had two similarly affected eyes of which one was treated. The treated eyes retained significantly better visual acuity than the untreated ones. Treated eyes deteriorated by 1 or 2 Snellen lines significantly less often than did untreated eyes. 8 treated and 18 untreated eyes became blind. Prognosis was best in those with initial visual acuity of 6/24 or better.