The objective of this study was to assess the validity of the mass balance (MB) approach for predicting DBP formation in feed/permeate blends. This was accomplished by collecting feed and permeate samples from several full-scale, pilot-scale and/or bench-scale systems that were treating waters representative of those evaluated during the ICR treatment studies. These feed and permeate samples were blended at four different feed/permeate ratios. The feed, permeate and blended water samples were characterized using a wide range of water quality parameters, chlorinated, and analyzed for the formation of four trihalomethanes and up to nine haloacetic acids. Finally, the measured concentrations in the blended samples were compared to the MB predicted concentrations for all analytes. Includes 5 references, tables, figures.