ABSTRACT2, 4, 5‐THBP (2, 4, 5‐trihydroxybutyrophenone) is a substrate for mushroom tyrosinase with a Kmvalue of 1.00 mM. The final product(s) formed is red (λ.max480–490 nm) and it is rather stable with time. An intermediate red product(s), having a maximum at λ 505–515 nm, was detected and the time course of its conversion to the final red product(s) was studied. The data suggest that the intermediate red product(s) is 2, 4, 5‐THBP‐quinone which is converted to colorless polymerized 2, 4, 5‐THBP‐OH, which is then oxidized to a red polymerized 2, 4, 5‐THBP‐quinone(s), which is the