Schizophyllum commune. TLC and HPLC chromatogram showed that p-hydroxybenzoic acid was formed as a major degradation product of p-coumaric acid. The purity of p-hydroxybenzoic acid was further confirmed by mass spectrometry. A maximum amount 2.5 mg/l of p-hydroxybenzoic acid was detected in the culture medium on 12th day of incubation using 5.0 mM p-coumaric acid as sole source of carbon. It was assumed that during the process of p-coumaric acid degradation, p-hydroxybenzaldehyde was produced as an unstable intermediate, which was rapidly converted into p-hydroxybenzoic acid and accumulated in the media. An indication of a very slow reverse conversion, that is, p-hydroxybenzoic acid into p-hydroxybenzaldehyde was also traced.