An amperometric biosensor for the determination of phenol and chlorophenols using Trichosporon beigelii (cutaneum) has been developed. This sensor is more sensitive to chlorophenols, especially to mono- and dichlorinated phenols, than to phenol and is insensitive to benzoate. A linear relationship between the current range and the concentration of 4-chlorophenol is observed up to 40 mu mol/l. The detection limit for all substrates studied is 2 mu mol/l. The current difference is reproducible within 5.5% when the test solution contains 0.40 mu mol 4-chlorophenol.