This paper reports and discusses a laboratory experiment that tested the anaerobic fluidized bed (AFB) technology as a means for the treatment of concentrated industrial wastewater (wine distillery, vinasses) at thermophilic conditions. The purposes were to operate and characterize AFB under high organic loading conditions and to report on their steady-state performance. Experimentally, it was confirmed that AFB systems can achieve >82.5% chemical oxygen demand (GOD) reduction at a COD loading of 32.3 kg of COD m(-3) day(-1) for treating vinasses of wine. At hydraulic retention time (HRT) of 0.46 day, the volumetric rate of methane generation was 5.8 m(3) of CH4 m(-3) day(-1) with a methane yield of 0.33 m(3) of CH4/kg of COD removal. The greatest efficiency of substrate removal was 97% for an organic loading rate of 5.9 kg of COD m(-3) day(-1) and HRT of 2.5 days. The food-to-microorganism (F:M) ratio can be used as a parameter for treatment performance evaluation of AFB. For vinasses, excellent COD reduction and methane production were achievable at the F:M ratio of 0.55 kg of COD kg(-1) VSatt day(-1) (more than 80% of feed COD was removed, and 9 m(3) m(-3) day(-1) of methane was produced).