Paper-pulp-liquors and corrugated-paper-pulp-liquors were used as the bases for simulated papermill wastewater and were treated in anaerobic upflow filters which were operated at mesophilic (35 degreesC) and thermophilic (55 degreesC) temperatures. The hydraulic retention time (HRT) ranged from 11.7 to 26.2 h with organic loading rates (OLR) of 1.70-3.87 g/l per day. With the paper-pulp-liquors, the thermophilic digester showed significant increases in performance, based on soluble chemical oxygen demand (SCOD) removal, with increases in HRT, while the mesophilic digester showed virtually no increase. The specific methane production rates for the thermophilic digester were higher than those for the mesophilic digester at all the HRTs. With the corrugated-paper-pulp-liquors, the mesophilic digester had a performance which was appreciably worse than that of the thermophilic digester when the HRT was 12 h. The Stover-Kincannon equation was found to be applicable at both temperatures but the use of corrugated-paper-pulp-liquors was found to reduce the maximum utilisation rate (U-max) values considerably. (C) 2002 Elsevier Science Ltd. All rights reserved.