5,5-Dimethylhydantoin was prepared and allowed to react with an excess of acrylonitrile in dioxane in the presence of.potassium hydroxideas a catalyst, giving 1,3-di-(β-cyanoethyl)-5,5-dimethylhydantoin, which on hydrolysis in hydrcchloric acid was converted to 1,3-di-(β-carboxyethyl)-5-dimethylhydantoin. Reactions of acrylonitrile with compounds structurallys related to hydantoin, such as cyclic ureides, thiohydantoins and rhodanines, are now under investigation.