This study had four objectives: development of disinfection byproduct (DBP) formation profiles, determination of the major water quality and operational factors influencing those profiles, and the reliability of the profiles as predictive tools; the possibility of using the entry to distribution system (EPDS) total trihalomethane (TTHM) and total haloacetic acid (THAA) concentrations to predict formation at later distribution system locations; determination of compliance status with possible future regulations for each treatment plant in the study; and, comparison of DBP production with conventional vs. direct filtration treatment and pre vs. post chlorination. Samples were collected from ten water treatment plants and their distribution systems according to Information Collection Rule (ICR) sampling protocols. Nine of the treatment plants are participants in the ICR. However, all ten treatment plants participated in preICR sampling from late 1994 to 1996. Sample results from both preICR and ICR samples were included in the data set used in this paper.