Heating of 5-carbamoyl-(1) and 5-thiocarbamoyl-3-methyl-1-phenyluracil (5) derivatives in ethanolic sodium ethoxide causes a novel intramolecular rearrangement to give 5- anilinomethylenebarbituric acids (2) and 5-anilinomethylene-4-thiobarbituric and (6), respectively.