In this study, some hemorheological and coagulative parameters (blood viscosity, erythrocyte filtrability, CPA, platelet aggregation) have been evaluated in 40 patients with Chronic Respiratory Failure. The results obtained document in these patients, important hemorheologic changes. 11 patients with most serious rheologic changes have been treated with Pentossifillina. A significative improvement of the explored parameters and of the clinical condition has been checked after treatment.