Diphenylmethyleneaminooxycarboxylic acids were found to represent novel type inhibitors of the enzyme aldose reductase. Ester derivatives of the most active compound (3c) (IC(50)=33 microM) were prepared as potentialprodrugs and the rate of degradation was studied by treatment with buffers, plasma, and various hydrolytic enzymes. Whereas all compounds were not hydrolysed at physiological pH, incubation