A laboratory-scale reverse osmosis system was used to test the extent and rate of fouling generated by the treatment of membrane biological reactor effluent. System variables included two membrane types, the Hydranautics LFC-1 and the Trisep X-20; pretreatment with varying dosages of monochloramine or ultraviolet disinfection; and transmembrane pressure. Monitored responses in the concentrate and permeate included inorganic and organic analytes, pH, conductivity, total dissolved solids, and flux rates.Greater transmembrane pressure increased the fouling rate under all conditions. Less overall flux loss was observed for the X-20 at higher transmembrane pressure, however the addition of monochloramine induced greater flux loss on the X-20 relative to the LFC-1. The LFC-1 had higher rejection rates under all conditions, but had a higher overall fouling potential. The addition of 9.0 mg/L of monochloramine was observed to increase the critical fouling point of the LFC-1 membrane.