The removal of color and organic contaminants by adsorption on activated carbon from the effluent of a kraft pulp bleaching plant was investigated in a pilot plant. The caustic bleach effluent, which contains 80% of the color from pulp bleaching, was decolorized successfully when it was adjusted to pH 2.5. The spent carbon was regenerated with caustic solution for an average of 11 adsorption-regeneration cycles before thermal regeneration was required. Variables studied included pH of feed, feed rate, effluent from bleaching of hardwood and softwood, caustic requirements for regenerating the carbon, and concentration of color in feed. Capital and operating cost estimates for a full-scale plant are presented. The cost effects of variations in design and operating conditions are also discussed. Conclusions are that the process is technically sound, that it will remove 94% of the color and 84% of the total organic carbon from caustic bleach effluent from the bleaching of softwood, but that it has slightly higher capital and operating costs than alternative methods for reducing color in bleach effluents (resin adsorption, ultrafiltration, or bleach sequence modifications, for example).