Since the deletion of federally mandated fecal coliform limits from the definition of secondary wastewater treatment in 1976, most states have been reviewing and modifying their requirements concerning wastewater disinfection, particularly with regard to the use of chlorine. One of the issues involved in this review of disinfection policies has been the discharge of potentially carcinogenic halogenated organic compounds formed during chlorination and their effect on aquatic life and downstream water consumers. This research examined the formation of THMs and TOX during wastewater chlorination at three wastewater treatment plants in the Piedmont area of North Carolina. In-stream water samples were taken upstream and downstream from two of the plants to determine the increase and persistence of THMs and TOX below each plant. TOX and THM formation was evaluated in terms of effluent wastewater quality, chlorine contacting system, method of chlorine addition, and chlorine-to-ammonia ratio. The results showed that between approximately 50 and 150 ug/l of TOX was formed as a result of chlorination at the three plants; small to insignificant levels of THMs were detected. A significant amount of the final discharge level of TOX was present in the unchlorinated secondary effluent which indicates that halogenated organics formed during drinking water chlorination may be a major contributor . TOX was shown to be conservative in the respective receiving streams by mass balance calculations and agreement of the two downstream sampling stations.