The effectiveness of adding powdered activated carbon to activated sludge systems was evaluated for enhanced removal of specific toxic organic compounds. Nine organic compounds encompassing a range of solubility, volatility, biodegradability, and adsorptive properties were studied along with selected commercial powdered activated carbons. The studies showed that the addition of less than 100 mg/l powdered activated carbon did not enhance the removal of the biodegradable compounds benzene, toluene, ethylbenzene, o-xylene, chlorobenzene, and nitrobenzene. Significantly improved removals of the poorly degradable and non-biodegradable compounds 1,2-dichloro-benzene, 1,2,4-trichlorobenzene, and lindane, occurred at influent powdered carbon concentrations in the 12.5- to 25-mg/l range. Influent powdered carbon concentrations of 100 mg/l effected overall removals of greater than 90%.