In order to comply with the Disinfectants/Disinfection Byproducts Rule, many utilities are minimizing free-chlorine contact time and/or implementing chloramination. In bench-scale tests with short free-chlorine contact times (<1 h) and post-chloramination (24 and 72 h), trihalomethane (THM) formation resulted from a combination of pre-chlorination and postchloramination. THM formation at 25 or 10C in the presence of chloramines was 16 or 35 percent, respectively, of what would have formed in the presence of chlorine during 24- and 72-h contact times. In these tests, haloacetic acid (HAA) formation was relatively unchanged by postchloramination, except when the bromide was quite high (0.35-0.5 mg/L). These tests can be used to estimate THM and HAA formation during full-scale operation with short free-chlorine contact times (to achieve 1 log of Giardia inactivation) followed by chloramination. In addition, these data were used to refine previously developed equations for the prediction of THMs during both short- and long-term chlorination and chloramination (contact times of minutes to days). Includes 13 references, figures.