The Authors studied the behaviour of lung volumes and mechanics and of haematocrit after intermittent pulmonary positive pressure breathing (IPPB) in patients with chronic obstructive lung disease. An improvement of obstructive sindrome at 10'-20'-40' and a contemporary decreasing of haematocrit were observed. This statistically significant modification was regarded as an expression of a different distribution of blood in lung vessels dued to an increasing of this vascular compliance and to a decrease of alveolar inflation. The Authors postulate the realization of a better circulation in lung vessels which contributes to a lowering of haematocrit in these patients perhaps for a different VA/Ob ratio.