A laboratory-scale anaerobic reactor in which the bottom two-thirds were occupied by a sludge blanket and the upper one-third by submerged small cubes of polyurethane foam, was evaluated for the anaerobic treatment of slaughterhouse wastewater The reactor was operated at 35 degrees C during the two experimental studies. In the first study, the chemical oxygen demand (COD) concentration of the wastewater was increased from 3.74 to 10.41 gl(-1) whilst maintaining a constant hydraulic retention time (HRT) of 1.5 days. In the second, the HRT was decreased from 1.35 to 0.50 days, whilst maintaining a constant influent COD concentration of 10.41 gl(-1). The results showed that this type of reactor was suitable for the anaerobic treatment of this wastewater and demonstrated a high COD removal of between 90.2 and 93.4% at organic loading rates between 2.49 and 20.82g COD l(-1) day(-1). At an HRT of 0 5 days, the reactor achieved a methane yield of 0.345 l CH4 STP per gram of COD removed. This yield is higher than the values reported in previous studies.