ABSTRACTHorseradish peroxidase in the presence of hydrogen peroxide oxidizes kojic acid (5‐hydroxy‐2‐hydroxymethyl)‐4H‐pyran‐4‐one) to a yellow product(s). The yellow product(s) formed has a major absorbance peak at 375 nm and is fluorescent. The relationships between, and effects of, various concentrations of horseradish peroxidase, kojic acid and hydrogen peroxide on the rate of oxidation of kojic acid to the yellow product(s) are described. The observation that the oxidation of kojic acid to the yellow product(s) occurs best in the presence of very low concentrations of hydrogen peroxide, relative to that of kojic acid, suggests that kojic acid is a poor hydrogen donor (AH2) for horseradi