This paper summarizes the results of a 1987 joint Ontario pulp and paper industry study of the composition of mill effluents with respect to parameters on the U.S. EPA priority pollutants list, conventional parameters and toxicity. The results of this study demonstrated that pulp and paper mill effluents contain few priority pollutants. These results, together with other data, will be used in the development of the sector's Effluent Monitoring Regulation under Ontario's MISA program.