The aim of this study was to investigate the effect of pure cultures on the enhancement of biological phosphorus removal capability of a Sequencing Batch Reactor (SBR) inoculated initially with a mixed culture. For this purpose, three anaerobic/aerobic SBRs with mixed cultures were started in parallel and operated for a while. At the end of this period, pure cultures of Acinetobacter lwoffii, A. lwoffii-Pseudomonas aeruginosa mixture and P. aeruginosa were added into the first, second and third reactors, respectively. All reactors were operated at a constant solid retention time (SRT) of 10 days and the food/microorganism (F/M) ratio was changed between 0.43-0.50 mg COD mg(-1) VSS day(-1). The total cycle time was 14 h throughout the experimental study. The addition of A. lwoffii to the mixed culture in the first reactor significantly enhanced the biological phosphorus removal (EBPR) rate. Complete removal (E = 100%) of 20 mg 1(-1) PO4-P was achieved within 35 days of operation. Corresponding removal efficiencies obtained using A. lwoffii-P. aeruginosa mixture (second reactor) and P. aeruginosa alone (third reactor) were 25% and 20%, respectively. The COD removal efficiency was 90% in all reactors. (c) 2004 Elsevier Ltd. All rights reserved.