A laboratory scale upflow anaerobic sludge blanket (UASB) reactor was operated at 35 degreesC for over 200 days to investigate the granulation mechanism during tetrachloroethylene (TCE) biodegradation. Anaerobic, unacclimated sludge and glucose were used as seed and primary substrate, respectively. TCE-degrading granules developed after 1.5 months of start-up. They grew at an accelerated pace for 7 months. The TCE-degrading granules had a maximum diameter of 2.5 mm and specific methanogenic activity of 1.32 g chemical oxygen demand (COD) g(-1) total suspended solid (TSS) day(-1). 94% COD and 90% TCE removal efficiencies were achieved when the reactor was operating at loading rates as high as 160 mg TCE l(-1) day(-1) and 14 g COD l(-1) day(-1), after 230 days of continuous operation.