Anthranilic acid (1 mol.) reacted in pyridine solution with benzoyl chloride (2 mol.) to give 2-phenyl-4H-3,1-benzoxazin-4-one in high yield. With 1 mol. of benzoyl chloride, however, a mixture of benzoxazinone and N-benzoylanthranilic acid was obtained. The mechanism of the reaction has been investigated and various 2-substituted-4H-3,1-benzoxazin-4-ones have been prepared and their u.v. spectra recorded.