An investigation has been made into whether charcoal hemoperfusion stimulates a hyperplastic response in the liver of the normal rat. Animals underwent hemoperfusion over Norit RBX1 (Strathclyde, Glasgow, U.K.) charcoal granules using a technique which allowed perfusion in the unrestrained and conscious state. Controls consisted of animals subjected to perfusion through empty columns and animals cannulated only. Body weight, liver weight, function, and DNA synthesis were recorded at various times after completion of perfusion and control procedures. The results indicated that charcoal hemoperfusion did not stimulate a hyperplastic response in the liver of the normal rat following perfusion, and did not produce marked changes in body weight, liver weight, and function.