The endogenous processes in anaerobic end and aerobic end sludge responsible for biological denitrifying phosphorus removal were compared during a 7-d starvation under anaerobic conditions. The results showed that polyphosphate and glycogen were utilized simultaneously to generate maintenance energy for both the anaerobic and aerobic end sludge. During the 7-d starvation, the decay rate of denitrifying-phosphorus-accumulating-organisms (DPAOs) was higher for the aerobic end sludge than for the anaerobic end sludge. More energy was required for maintenance in the aerobic end sludge than for the anaerobic end sludge, with the greater amount of phosphorus release and glycogen degradation occurring in the aerobic end sludge. Moreover, different metabolic pathways for the endogenous processes were observed for the anaerobic and aerobic end sludge. After the 7-d starvation, the activity of DPAOs decreased more for the aerobic end sludge than that for the anaerobic end sludge. (C) 2011 Elsevier Ltd. All rights reserved.