The level of lipid peroxide (LPO) in glucocorticoid-induced cataractous lenses was measured by using thiobarbituric acid. When 0.25μmol of hydrocortisone hemisuccinate sodium (HC) were administered to 15-day-old chick embryos, the level of LPO in the lens increased to approximately 1.4-fold of the control level at 24 to 48 hr after HC treatment. However, the level returned to the control level by 96 hr with the disappearance of opacity in the lens. A triple application of ascorbic acid (20μmol/egg) at 3, 10 and 20 hr after HC treatment prevented cataract formation and elevation in the level of LPO in 60% of the lenses. In 40% of the eggs treated with HC plus ascorbic acid, the results were no different than HC alone. Treatment with prednisolone hemisuccinate sodium (0.25μmol/egg) produced an elevation in the level of LPO in the lens but that with cortisone hemisuccinate sodium or cortexolone hemisuccinate sodium did not change the level of LPO in the lens. The phenomena of the cataract formation and the elevation of LPO in the lens caused by HC seemed to be related to each other and due to its glucocorticoid activities.