By means of 370 spirographic tracings made on 170 patients with acute brain injuries seven respiratory forms are described - irregular-normal, marked irregular, periodic, heaving, sighing, regular and gasping respiration - the respective prognostic value being discussed. In all these forms of respiration the respiratory minute/volume was found to be either normal or too small or uneconomically exaggerated. In order to prove whether in these different respiratory rhythms there is a distinct behaviour of the respiratory control, the sensitivity of the nervous centers was studied by the relationship between the respiratory minute/volume and the increasing arterial CO2 pressure. These studies lead to the conclusion that owing to acute cerebral injuries, and independently of the respiratory rhythm, hypo or hyperexcitability of the respiratory centers and consequently hypo or hyperventilation may occur, both harmful to oxygenation of brain tissue. Clinical observations associated with these investigations have shown that an increased sensitivity of respiratory centers determinating hyperventilation is mostly connected with muscular hypertonus, extensor spasms and/or convulsions; cases of brain damage with hypoexcitability of respiratory centers and pulmonary hypoventilation are connected with generalized muscular hypotonia. For therapeutical purposes pharmacological sedation with neuroplegic drugs and/or short acting anesthesia must be employed in cases with muscular hypertonus and hyperventilation; on the contrary, in cases with muscular hypotonia and hypoventilation the sedation must be as minimal as possible and cautious.