Researchers conducted prelimary enchanced coagulation tests at the Metropolitan Water Distict of Southern California's (MWDSC's) 5.5-mgd demonstration plant from August to October 1992. California State project water and Colorado River water were tested. The first goal was to determine whether this mode of operation is an effective strategy for controlling disinfection byproducts (DBPs) and DBP precursors at MWDSC facilities. If this strategy proved to be successful, the second objective was to estimate the additional operational costs of complying with the proposed Disinfectants/DBP Rule and to identify the coagulation conditions that minimize these costs. Although the results show that enhanced coagulation can meet the criteria being considered for the rule, this process will increase MWDSC's cost of treatment. Includes 19 references, tables, figures.