1. Oxidation of methyl retinoate with monoperphthalic acid gave methyl 5,6-epoxyretinoate, obtained as pale-yellow crystals, m.p. 89 degrees . 2. The structure of the epoxide was confirmed by its ultraviolet, infrared, nuclear-magnetic-resonance and mass spectra. 3. The biological properties of the epoxide were investigated in male and female rats, and were found to be qualitatively similar to those of retinoic acid and methyl retinoate. 4. When administered to male rats reared on a vitamin A-free diet, the epoxide permitted growth although it did not maintain good general health. 5. Rats given a vitamin A-free diet and supplements of the epoxide had degenerate testes. 6. Female rats, maintained on a vitamin A-free diet containing retinoic acid and given supplements of the epoxide during pregnancy, resorbed their foetuses and failed to deliver litters. 7. The threshold of the electroretinogram response in male rats reared on a vitamin A-free diet with supplements of the epoxide was elevated above normal and was similar to that of rats maintained with methyl retinoate. 8. The oral administration of the epoxy acid to rats did not result in the accumulation of the corresponding epoxy alcohol in their livers.
