This study aimed to evaluate the effect of high organic loading rates (OLR) (60.0-480.00 kg COD m (3) d (1)) on biohydrogen production at 55 degrees C, from sugarcane stillage for 15,000 and 20,000 mg COD L (1), in two anaerobic fluidized bed reactors (AFBR(1) and AFBR(2)). It was obtained, for H-2 yield and content, a decreasing trend by increasing the OLR. The maximum H-2 yield was observed in AFBR(1) (2.23 mmol g CODadded1). The volumetric H-2 production was proportionally related to the applied hydraulic retention time (HRT) of 6, 4, 2 and 1 h and verified in AFBR1 the highest value (1.49 L H-2 h (1) L (1)). Among the organic acids obtained, there was a predominance of lactic acid (7.5-22.5%) and butyric acid (9.4-23.8%). The microbial population was set with hydrogen-producing fermenters (Megasphaera sp.) and other organisms (Lactobacillus sp.). (C) 2014 Elsevier Ltd. All rights reserved.