Two biosensors based on Trametes versicolor laccase (TvL) were developed for the determination of phenolic compounds. Commercial oxygen electrode and ferrocene-modified screen-printed graphite electrodes were used for preparation of laccase biosensors. The systems were calibrated for three phenolic acids. Linearity was obtained in the concentration range 0.1-1.0 mu M caffeic acid, 0.05-0.2 mu M ferulic acid, 2.0-14.0 mu M syringic acid for laccase immobilised on a commercial oxygen electrode and 2.0-30.0 mu caffeic acid, 2.0-10.0 mu M ferulic acid, 4.0-30.0 mu M syringic acid for laccase immobilised on ferrocene-modified screen-printed electrodes. Furthermore, optimal pH, temperature and thermal stability studies were performed with the commercial oxygen electrode. Both electrodes were used for determination of a class of phenolic acids, achieving a cheap and fast tool and an easy to be used procedure for screening real samples of human plasma. (c) 2006 Elsevier B.V. All rights reserved.