BACKGROUND: Laccase is an intensively researched enzyme for industrial use. Except for decolorization measurements, high performance liquid chromatography (HPLC) analysis is the conventional method for monitoring the phenolic removal during laccase enzyme reaction. This paper reports an investigation of the continuous UV absorbance follow-up of the laccase reaction with steam pretreated poplar hydrolysate. RESULTS: Vanillin was used as a model substrate and lignocellulose xylose rich fraction (XRF) as a biologically complex substrate for laccase detoxification. The reaction was followed by HPLC-UV as well as by UV spectrometric measurements. Results suggest that the reaction can be successfully monitored by measuring the change of UV absorbance at 280 nm, without previous compound separation. In the case of XRF experiments the spectrophotometric follow-up is especially useful, as HPLC analysis takes a long time and provides less information than in the case of single substrates. The method seems to be suitable for optimization and process control. CONCLUSION: The results obtained can help to construct a fast, easy and straightforward monitoring system for laccase-phenolic substrate reactions. (C) 2015 Society of Chemical Industry