Six-week-old rats received 8 kJ/m(2) ultraviolet B (UVB) for 15 min. For the intervention in cataract development, intraperitoneal injection of melatonin (4 mg/kg daily for 1 week) following UVB exposure was performed. Lenticular calcium and magnesium levels were determined in UVB + melatonin, UVB and control groups. One week after exposure, significantly more cataractous changes were observed in the UVB group than the UVB + melatonin group. The mean lens calcium and magnesium levels for the UVB group were significantly higher than those for the control and the UVB + melatonin groups. There were no significant differences between the control and the UVB + melatonin groups for the mean lens calcium and magnesium levels. Copyright (C) 2000 S. Karger AG, Basel.