A study has been made of thermophilic aerobic biodegradation of the liquid fraction of potato slops (distillation residue) from a rural distillery. The COD of this fraction ranged from 49 to 104 g O2/l, the main contributions to the COD coming from organic acids, reducing substances, and glycerol. It was found that biodegradation could be divided into the following stages: organic acids were removed first, followed by reducing substances and glycerol. The extent of removal varied according to the process temperature. At 50 degrees C, acetic and malic acids were removed completely, but the amount of isobutyric acid increased. At 60 degrees C, organic acid removal ranged from 51.2% (isobutyric acid) to 99.6% (lactic acid). Removals of glycerol and reducing substances were 86.2% and 87.4%, respectively. COD reduction was also temperature dependent, the highest removal efficiency (76.7%) being achieved at 60 degrees C. Dissolved oxygen may have limited the biodegradation process, as indicated by the DOT-versus-time profile.