The anaerobic treatment of salty cheese whey was investigated using horizontal and vertical shaft types of anaerobic rotating biological contact (ARBC) reactors to determine the effects of the hydraulic retention time (HRT) and the type of rope used to form the fixed-film structure on the rotating discs. Optimal performance was obtained with the vertical shaft-type ARBC reactor operated at 3-d HRT and 37 degrees C, using cotton rope to form the fixed-film structure. Maximum gas production of 4.1 l/l digester.d with a methane content of 74% and COD reduction of 85% were achieved.