A description of a selective ventilation distribution circuit (S.V.D.C.). The use of this circuit is illustrated by the description of 5 cases where the following were applied: 1 - the measurement of tidal volume of pressures for each lung during the respiratory cycle; 2 - regulation of tidal volumes to be as appropriate as possible for the patient; 3 - the application of different degrees of PEEP for each lung. This circuit is easy to construct and manipulate. It is connected to the patient via a double lumen endotracheal tube (Carlens) and uses only one respiratory.