A laboratory scale activated sludge treatment system was developed for the treatment of phenoxy herbicide chemicals and the associated chlorophenols in a toxic landfill leachate. A novel sludge recycle system was employed to ensure high specific activity of the return sludge. The activated sludge treatment resulted in 99.5% removal of phenoxies and chlorophenols and 84% TOC reduction for 10% influent leachate concentrations. The corresponding toxicity reduction was 76%. An increase in influent concentration resulted in a decline in activated sludge performance.