A 40% total body scald burn was produced in mature rats. An immediate decrease of the metabolic rate was followed by a hypermetabolic response similar to that described in human beings following thermal injury. The amounts of adenine nucleotides and hexosemonophosphates were monitored in three types of cells: erythrocytes (which lack mitochondria), skeletal muscle cells (which to a certain extent can rely on an increased glycolysis for their increased energy supply) and liver cells (which are sensitive to hypoxia and have a great need of energy in the post-traumatic period). Only in the liver did the energy charge derived from the individual concentrations of adenine nucleotides change significantly, but remained virtually constant in muscle cells and erythrocytes despite a change in total oxygen consumption, from minus 85% (in the early phase) to plus 30% (in the later phase) of the expected value. Altered energy metabolism in liver and muscle tissues is related to wound healing, whereas the biochemical changes in erythrocytes is related to the degree of haemolysis of younger cells induced by the thermal injury.