Impaired hemorrheological properties may worsen the tissue hypoxia distal to an arterial narrowing in patients with peripheral arterial occlusive disease (PAOD). The objective of this study was to investigate the changes in red blood cell rigidity, blood viscosity and plasma viscosity as contributing factors in the development of hypoxia in patients with critical limb ischemia (CLI).Forty patients with critical limb ischemia and 40 healthy subjects were included in the study. The subjects included in the study were non-diabetic with blood pressure measurements within the normal range. Compound known to interfere with hemorrheological parameters were not taken by the patients for at least 7 days prior to investigation. Routine blood counts (WBC, RBC, Hb, Hct), plasma fibrinogen levels, plasma total cholesterol levels, red blood cell rigidity, blood and plasma viscosity were determined in both groups. Statistical evaluation of the results of both groups was compared by student's "t"-test. The level of significance was set at p<0.05.Blood viscosity at a shear rate of 6.00 sec(-1) was found to be significantly lower in the CLI group (p<0.001), whereas no significant difference was encountered when blood viscosity was measured at a shear rate of 225 sec(-1). Plasma viscosity and plasma fibrinogen levels were comparable. Plasma total cholesterol levels were found to be significantly higher in the CLI group (p<0.05) and red blood cell rigidity significantly lower (p<0.001).These findings may provide new insights into the role of blood viscosity in patients with CLI contrary to the previous reports in the literature. Therapies that address red blood cell rigidity more directly may decrease tissue hypoxia distal to arterial narrowing by preventing hemolysis, improving microcirculation, and increasing oxygen carrying capacity and may be more beneficial for these patients.