By using appropriate 14C-labelled phenolic substances as precursors in feeding experiments the following steps in barnol biosynthesis have been established: acetate + malonate leads to 2,4-dihydroxy-6-ethyl-5-methylbenzaldehyde leads to 1,3-dihydroxy-4,6-dimethyl-2-ethylbenzene leads to barnol. P. baarnense can also reduce orcylaldehyde and 2,4-dihydroxy-5,6-dimethylbenzaldehyde to dimethylresorcinol and trimethylresorcinol, respecitively.