Summary.The cytoloxlc efTects of hyperthermia on tumours are readily measured. l';iramelers of injury to normal tissues are needed to evaluate therapeulic potential.Fifty-five isolated rat livers were perfused in vitro for 180 min in order to determine parameters of hyperthermic injury. During this period they were heated for I h at lemperaiures ranging from 37° to 45° and then assessed for evidence of hyperthermic injury.The most critical indicator of hyperthcrmic injury was sustained depression of bile production. Bile sccreiion decreased by 80% after heating at temperatures above 42°. A^partate amino transferase (AST) release increased significantly at temperatures of 42° and above.Potassium and variable amounts of glucose were released into the medium during heating, reflecting temporary changes in melabolism at high temperatures.

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