The plasma levels of adrenaline and noradrenaline were measured by a radioenzymatic method in 3 patients with accidental hypothermia and followed up until normal body temperature was achieved. In all 3 patients the hypothermia was accompanied by markedly elevated levels of noradrenaline, whereas adrenaline increased considerably only in one of the 3 patients. During normalization of body temperature the elevated catecholamine levels started to decrease. In 2 of the 3 patients nearly normal catecholamine levels were measured, when body temperature had normalized. In spite of the high levels of catecholamines in plasma the heart rate was strikingly low at the lowest temperature. During the increase of the lowered body temperature the heart rate increased in contrast to the decreasing catecholamine levels. The increase of the catecholamine levels in plasma in patients with accidental hypothermia can be explained either by an augmented stimulation of the sympathetic nervous system or by a decreased metabolism. On the basis of the high endogeneous catecholamine levels the use of beta-sympathomimetics appears contraindicated in case a haemodynamic insufficiency develops during the course of accidental hypothermia.