METHODS Twenty-four male and female people have been examined. They were afflicted with respiratory failure; on blood gas analysis they have been divided into two groups: hypoxic and hypoxic-hypercapnic subjects, disregarding the base pathology. We have used both the rotatory and double filtration methods, using a constant 15 cm water filtration pressure. The following rheological values have been defined: plasmo-erythrocytic viscosity, plasmatic viscosity, erythrocytic viscosity and erythrocytic deformability. The values have been expressed in cP. We have also considered haemacytometric parameters. RESULTS It came out that all the rheological parameters were highly different in both groups, with an increase of, more or less, 30% in plasmo-erythrocytic viscosity; a four times increase of erythrocytic viscosity compared to normal values and a decrease of 60% in erythrocytic deformability. The plasmatic viscosity was also very increased: we must correlate this phenomenon with phlogotic or neoplastic pulmonary pathology of the people we have examined. Regarding haemacytometric parameters, from the hypoxic-hypercapnic group comes out significant higher MCV values and MCHC lower ones, with a higher anisocytosis level. CONCLUSIONS From these results we think that the altered systemic rheology makes hypoxic condition wider, while, at pulmonary level, help the haemodynamic resistances to increase, with the onset of a hypertensive condition.