The sequencing batch reactor (SBR) process is known for its flexibility to meet a wide range of treatment needs, including nutrient removal. However, information related to the operational stability of SBR nutrient removal systems and control parameters to adjust the cyclic duration is sparse; Consequently, this study was undertaken to identify process parameters (pH and oxidation reduction potential) that could be useful for monitoring and real-time control purposes. In general, the system achieved removal efficiencies of 91, 98 and 98%, respectively, for Chemical Oxygen Demand, total nitrogen and phosphate at the solids retention time of 10 days, with a cyclic duration of 6 h. Shock loadings of nitrogen (20 mg dm(-3) of NH4+-N, four cycles) exhibited little impact on effluent quality, except for a higher nitrate content. Activated sludge settled well throughout the entire study period. Several significant points associated with different reactions within SBR cycle, e.g. end of nitrification, end of phosphate release and completion of phosphate uptake, were identified in pH profiles. Slope changes in pH profiles (dpH/dt, or d(2)pH/dt(2)) were found to better represent the corresponding biological reactions. The application of these significant points in pH profiles as real time control parameters appears promising.