NEW MATERIAL:The benzoquinone derivative of formula I [n is 1 or 2; R is H or (substituted alkyl or acyl].

EXAMPLE: 6-Hydroxymethyl-2,3-dimethoxy-5-methyl-1,4-benzoquinone.

USE: It has protocollagen.proline hydrolase inhibiting and collagen biosynthesis suppressing activities, and is useful as an animal tissue fibrosing suppressing agent for the prevention and remedy of the organofibrosis of animals, especially mammals such as rabbit, dog, human, etc. For example, the compound is useful as a remedy for pulmonary fibrosis, hepatocirrhosis, nephrosclerosis, arteriosclerosis, scleroderma, etc.

PROCESS: The compound of formula I can be prepared by reacting, e.g. the compound of formula II with the peroxide of the carboxylic acid of formula III or its anhydride in an inert solvent such as n-hexane, toluene, etc. at 80W100°C.