In the case of patients with unilateral lung disorders one must anticipate a further increase in the intake volume of the more elastic lung and a decrease in intake volume of the less elastic lung when the inspiratory pressure is increased or the inspiratory time is extended within the framework of mechanical ventilation. Therefore, differential pulmonary ventilation lends itself for the treatment of unilateral damage of the lung by enabling the selective application of a positive end-expiratory pressure or an inverse inspiratory time. For a better understanding of the overlapping pathophysiologic reactions, the changes in lung mechanics, haemodynamics and gas exchange were measured on the healthy lung with unilateral application of a positive and expiratory pressure or an increased inspiratory time. Thirteen male and female patients, who had to undergo intracranial surgery were ventilated with two synchronized servoventilators using a Carlens tube. The positive end expiratory pressure varied in the right lung in spans of 6 cm each, 0-12 cm H2O, inspiratory time varied 34-70%. The left lung was ventilated with a 35% inspiratory time and an end expiratory pressure of 0. The respiratory intake volume was divided up into 45% (left lung) and 55% (right lung) based on the physiological difference in size between the left and right lung. Our results show that a directed unilateral application of a positive end expiratory pressure or an increased inspiratory time does not have any relevant damaging effects on the other lung. It can be expected that in the case of non-differentiated mechanical ventilation the ensuing unequal distribution of alveolar ventilation and perfusion with consecutive increase of intrapulmonary shunt volume can be decreased by the discriminate treatment of each lung.