An anaerobic filter (5.8 m(3)) operated at ambient temperature was used to treat brewery wastewater: The hydraulic retention rime was maintained at a constant value (10 h) throughout the trial. The start-up period, to achieve fully stabilized conditions was 6 months. At an applied loaning rate of about 8 kg COD/m(3)d, the mean COD removal was 96% and the mean gas production was 7.1 m(3)/d. The methane content of the biogas was higher than is normally found. During the steady state regime it was 80-95%. The results show that, when the ambient temperature is high, an anaerobic filter can operate in the mesophilic range and be used to treat brewery wastewater successfully.