A simulated textile ef¯uent (STE) was generated for use in laboratory biotreatment studies; this ef¯uent contained one reactive azo dye, PROCION Red H-E7B (1.5 g dm À3 ); sizing agent, Tissalys 150 (1.9 g dm À3 ); sodium chloride (1.5 g dm À3 ) and acetic acid (0.53 g dm À3 ) together with nutrients and trace elements, giving a mean COD of 3480 mg dm À3 . An inclined tubular anaerobic digester (ITD) was operated for 9 months on the STE and a UASB reactor for 3 months. For a 57 day period anaerobic ef¯uent from two reactors, a UASB and an ITD, was mixed and treated in an aerobic stage. In days 77± 247 68% of the true colour of PROCION Red H-E7B was removed by anaerobic treatment with no colour removal aerobically and up to 37% COD was removed anaerobically, with a corresponding BOD removal of 71%. For combined anaerobic and aerobic treatment a mean COD removal of 57% and BOD removal of 86% was achieved. Operation of the ITD at a 2.8 day HRT (volumetric loading rate (B v ) 1.24 g COD dm À3 day À1 ) and the UASB at a 2 day HRT (B v 1.74 g COD dm À3 day À1 ) gave comparable COD removals but the UASB gave better true colour removal. Ef¯uent from the combined process operating on this simulated waste still contained an average 1500 mg COD dm À3 , and further treatment would be required to meet consent standards.