A study was conducted to evaluate the biological nutrient removal performance of three full-scale sequential batch reactor (SBR) plants. The plants were designed to handle an average flow of 0.023, 0.025, 0.001 m(3)/s, respectively. These SBR systems were designed to achieve nitrification, denitrification and biological phosphorus removal. Influent and effluent samples were analyzed for CBOD5, TSS, ammonia nitrogen, nitrate nitrogen, total phosphorus, pH and temperature. The SBR performance data show that typical SBR designs can meet effluent CBOD5 and TSS concentrations of less than 10 mg/l. With some additional design modifications, SBRs can successfully nitrify to limits of 1-2 mg/l NH3-N. They also appear to achieve phosphorus removal, if desired, without chemicals addition to less than 1.0 mg/l.