The hemorheologic abnormalities were studied in patients suffering from thromboangiitis obliterans (TAO) and compared findings with those of patients suffering from critical limb ischemia because of peripheral atherosclerotic obstructive disease (PAOD) and the healthy subjects. This prospective study included 20 patients with TAO, 20 patients with PAOD, and 20 healthy subjects. Hematocrit, plasma fibrinogen, red blood cell rigidity, and blood and plasma viscosity were determined in all groups. Hematocrit values of the TAO group were significantly higher than those of the PAOD group and the control group (p<0.001 and p<0.001, respectively). BV at a shear rate of 6.00 sec(-1) was higher in TAO than the PAOD and control (p<0.01 and p<0.05, respectively). BV at a shear rate of 225 sec(-1) was higher in the TAO and PAOD than the control (p<0.001 and p<0.001, respectively) and also PAOD values were higher than the TAO (p<0.05). RBC rigidity was higher in the TAO and PAOD than the control (p<0.001 and p<0.05, respectively) and these values were higher in PAOD than the TAO (p<0.05). These results show the impairment in hemorheologic parameters in TAO may provide a new insight into the treatment of patients with TAO in the active period of the disease.