The sewage treatment plant of the city of Hagerstown, Maryland--a manufacturing city with about 130 industrial firms, which are classified in more than 25 different product categories--receives for treatment domestic sewage and a diversity of industrial waste and process waters. Some of these industrial wastewaters exert high immediate and ultimate oxygen demands that could not be satisfied by the treatment plant. Therefore, certain methods of 'pretreating' the city's combined wastewaters to render these waters more amenable to treatment by the existing treatment plant were tried and evaluated. The pretreatment methods tested were intended to assist the plant in meeting the oxygen demands by providing initial oxidation. The methods were: diffuse aeration with and without the addition of waste activated sludge, chlorination, addition of sodium nitrate, and the addition of potassium permanganate. Ammoniation was also tried in an effort to destroy some of the more noxious industrial materials in the wastewaters. Both aeration and chlorination proved to be effective methods of pretreatment, with the efficacy of aeration being enhanced somewhat by the addition of waste activated sludges. Both methods increased the BOD5 removal efficiency of the plant under dry-weather conditions from less than 70% to better than 90%.