We found that amizol (amitrol, 3-amino-1H-1,2,4-triazole) is a potent cataractogenic agent. Cataract is produced in a group of young Dutch rabbits which daily consumed 0.2% amizol in drinking water and in a group of young littermate rabbits of the same strain fed on a special diet containing 0.2% amizol. Clinical picture of amizol cataract has been fully described. The decrease in catalase activity of lens capsule-epithelium is highest as compared to that of the corneal epithelium, liver, kidney, and blood in amizol-fed rabbits. Induction of cataract with a simultaneous fall in lens catalase by amizol in vivo indicates that this enzyme may have a significant role in metabolism of the lens. Since amizol is widelyused as a herbicide and cotton defoliant, its cataractogenic effect may be of public healthinterest.