Biogas production from sugarcane vinasse has enormous economic, energy, and environmental management potential. However, methane production stability and biodigested vinasse quality remain key issues, requiring better nutrient and alkalinity availability, operational strategies, and knowledge of reactor microbiota. This study demonstrates increased methane production from vinasse through the use of sugarcane filter cake and improved effluent recirculation, with elevated organic loading rates (OLR) and good reactor stability. We used UASB reactors in a two-stage configuration, with OLRs up to 45 g COD L-1 d(-1), and obtained methane production as high as 3 L L-1 d(-1). Quantitative PCR indicated balanced amounts of bacteria and archaea in the sludge (10(9)-10(10) copies g(-1) VS), and of the predominant archaea orders, Methanobacteriales and Methanosarcinales (10(6)-10(8) copies g(-1) VS). 16S rDNA sequencing also indicated the thermophilic Thermotogae as the most abundant class of bacteria in the sludge.