A stimulant-induced decrease in absorbance at 267 nanometers in preparations from rabbit olfactory epithelium requires ascorbic acid as a cofactor. Vitamin C is bound to proteins in the olfactory mucosa in vivo. When the stimulant. 3,7-dimethyl-6-octen-3-ol interacts with olfactory proteins, it triggers a change in protein conformation which renders ascorbic acid available for oxidation. The specific decrease in absorbance at 267 nanometers is produced when the "freed" ascorbic acid is oxidized.