BACKGROUND: The use of enzymes has attracted much interest for the decolourization of dyes from wastewater as an alternative to conventional treatments, which have limitations. Laccase can be used to decolourize dyes and its substrate range can be extended by inclusion of mediators. RESULTS: Sequential decolourization of reactive dyes was carried out by a laccase mediator system using as mediators violuric acid and 1-hydroxybenzotriazole. Violuric acid resulted in a high level of decolourization on the first and second cycles for reactive blue 114 (>= 95%), reactive yellow 15 and reactive red 239 (>= 80%), while for reactive black 5 a slightly lower value was observed (70%) on the second cycle. The degree of reactive blue decolourization remained at 90% after the third cycle, and at about 60% after seven cycles. With the other dyes decolourization decreased to 50-70% on the third cycle and further up to the final cycle (lower than 20%). When using 1-hydroxybenzotriazole as mediator a slight decrease in decolourization efficiency was obtained. Correlation between dye oxidation peak potential and dye degradation after 10 min reaction was obtained for both mediators. CONCLUSIONS: These results show that sequencing batch decolourization by laccase mediator system is a useful methodology for treating textile dying wastewaters with a high potential for application at industrial level. (C) 2008 Society of Chemical Industry