Summary Over five hundred samples of cheese, chiefly of the cheddar and Swiss types, were collected and analyzed for their carotene and vitamin A contents. The maximum vitamin A potency of cheddar cheese occurred in those samples made in the September–October period, 17.39 I.U. per gram (7900 I.U. per lb.); the minimum occurred in the March–April period, 7.94 I.U. per gram (3600 I.U. per lb.). The values for Swiss cheese were: August–October 14.67 I.U. per gram (6600 I.U. per lb.) and February–April 7.73 I.U. per gram (3500 I.U. per lb.). A few samples of cheese other than cheddar or Swiss were analyzed. Brick, Muenster, Limburger and Colby all showed no significant difference from cheddar cheese of the same season in vitamin A potency. No correspondence between vitamin A potency and grade of cheese was observed among the samples. The vitamin A potency of cheese corresponds to that of the milk from which it was made and this in turn reflects the carotene content of the ration.