The effects of oxygenated perfluorotributylamine (Fluosol-43) on the rheological properties of sickle (HbSS) erythrocytes have been determined by means of microviscometry and positive pressure cell filtration. Incubation of deoxygenated sickled erythrocytes (pO2 congruent to 30 mmHg) with oxygenated Fluosol-43 reduced the percentage of sickled erythrocytes from about 63 to 33%. Deoxygenation of 40% suspension of sickle erythrocytes in autologous plasma increased the viscosity by about 160% at shear rate of 1.15 sec-1. Incubation of the deoxygenated sickled erythrocytes with oxygenated Fluosol-43 significantly reduced the viscosity at the low shear rates. Filtration of 0.2% suspension of deoxygenated sickle erythrocytes through capillary-sized Nuclepore filters showed high resistance at low flow rates. Oxygenated Fluosol-43 increased the deformability of HbSS erythrocytes and thereby reduced the resistance at flow rates less than 1 ml/min. These data suggest that perfluorocarbons may be useful in reducing the propensity of hemoglobin S polymerization and sickling and thereby prevent tissue infarction in vaso-occlusive crisis. Therefore, the concept of examining the potential application of perfluorochemicals for alleviating severe vaso-occlusive events may be useful.