Irradiation of 3-hydroxy-l, 2-benzisoxazole (3) results in the formation of benaoxazolinone (4). This photoisomerization is shown to occur predominantly via the keto tautomer 3b since facile rearrangements of the N-alkyl-l, 2-beneisoxazolinones (19) occur under similar photolytic conditions. A mechanism involving a diradical species is proposed for this reaction. Low temperature photolysis-infrared measurements support this mechanism ...