Restart-up of an upflow anaerobic sludge blanket (UASB) reactor for the treatment of soybean processing wastewater was investigated. During the restart-up period, both chemical oxygen demand (COD) degradation efficiency and gas production rate increased. The specific methanogenic activity of anaerobic sludge and the fluorescence score for coenzyme F(420) in the effluent increased from 0.31 to 0.81 g-CH(4)-COD/gVSS/d and from 153 to 313, respectively. Among the various operating parameters the volatile fatty acids (VFA) and the CH(4) content were the first to become stable, which could be used as the main parameter for the reactor restart-up. The coenzyme F(420) also existed in the effluent and its concentration had a similar changing trend to the specific methanogenic activity value of the anaerobic sludge. Therefore, the F(420) fluorescence score in the effluent could be used to determine the methanogenic activity of anaerobic reactors. (C) 2009 Elsevier Ltd. All rights reserved.