A statistical analysis of the case material at the Intensive Care Unit, Freiburg, for the years 1975 and 1976 established that 40% and 39% respectively of patients with multiple injuries had also suffered a chest trauma and that the latter was the direct cause of respiratory insufficiency in 61% (1975) and 57% (1976) of patients in need of controlled respiration, i.e. respiratory insufficiency dominated the clinical and pathophysiological picture. The causes were: restricted respiratory movements due to pain, compression of the lungs or pathological changes in the injured lung, and they affected the normal gaseous exchange in a variety of ways. Alveolar hypoventilation with disturbance of ventilation-perfusion, increase in the functional shunt volume, rise in the functional dead space combined with reduced functional residual capacity and compliance result, if left uncorrected, in a drastic increase of resistance on the part of the pulmonary vessels and finally in, often fatal, hyoxaemia and hypercapnia. Regular estimations of the arterial blood gases in air and pure oxygen, of the arterio-alveolar difference in oxygen pressure, shunt volume, dead space and effective compliance of the chest wall and lungs are, therefore, essential. Treatment in an intensive care unit comprises the relief of any acute condition, such as tension pneumothorax, haemothorax, and general measures. Means to relieve pain in patients whose chest injuries are not sufficiently severe to require artificial ventilation are: intercostal blocking, acupuncture or peridural analgesia; efficient breathing exercises are important. The indications for artificial ventilation should be interpreted generously and the decision to perform it should be made at an early stage. The technique is determined by the type of pathological changes in the gaseous exchange and should aim at restoring normal conditions as far as possible.