The effect of cholestyramine in the daily diet upon the excretion of pentachlorophenol with the feces was studied in the rhesus monkey. The treatment increased fecal elimination of pentachlorophenol and/or metabolites up to 9- to 14-fold over a six-day period. At the same time urinary excretion was reduced 2- to 6-fold. The data suggest that cholestyramine interrupts the enterhepatic circulation of PCP and/or metabolites thus indicating its possible usefulness in preventing toxicity of PCP that otherwise may occur due to reabsorption of biliary PCP and/or metabolites.