When the basidiomycete fungus Polyporus tumulosus Cooke is grown as a surface culture on a glucose-salts medium, it produces a series of phenolic acid metabolites secreted into the culture liquor. Three of these (3,4-dihydroxyphenylacetic acid (I), 2,5-dihydroxyphenylglyoxylic acid (II), and 2,4,5-trihydroxyphenylglyoxylic acid (III)) were identified previously. During investigations aimed at elucidating the possible metabolic interrelationships of these compounds, further metabolites have been identified: p-hydroxybenzoic acid (IV), p-hydroxyphenylacetic acid (V), and 2,5-dihydroxybenzoic acid (VI) (well-known products of microbial activity), and small amounts of 3,4-dihydroxyphenylglyoxylic acid (VII)—to the authors' knowledge, this compound has not previously been reported as a fungal metabolite, although it has been cited as an intermediate in the breakdown of noradrenalin by chicken liver slices (Wada 1957). These minor metabolic products make only a transient appearance in the culture liquor, corresponding to a phase of active growth of the organism, and they are not discernible in liquors from aged or autolysing cultures. When liquor from 14-21-day-old cultures was examined spectroscopically, absorption peaks appeared at 254, 275, and 328 mp which could not be reconciled with those of known metabolites, and corresponding unknown spots appeared on paper chromatograms; these unknowns were subsequently isolated and identified as IV, V, and VI respectively by their characteristic properties and derivative preparation. Spots corresponding to at least two other phenolic compounds in very minute amount also made irregular appearances on chromatograms, and one of these (VII) was observed to be formed in greatly increased amount under certain conditions.