Hemorheological parameters were proved to be primary risk factors in ischemic heart disease (IHD) by several studies. In the present study the relation of these parameters to the severity of coronary artery disease (CAD) was examined. The data of 109 patients (mean age: 55 +/- 9 yrs) undergoing coronary angiography and 59 healthy controls (mean age: 35 +/- 10 yrs) were analyzed. Hemorheological parameters [hematocrit, fibrinogen level, plasma viscosity (PV) and whole blood viscosity (WBV)] were measured and circulatory index (CRI) was calculated. Patients were classified into three groups according to their coronary vessel state based on the coronary angiogram: Group 1 (n = 19, mean age: 53 +/- 8 yrs) without significant CAD, Group 2 (n = 19, mean age: 51 +/- 11 yrs) with single vessel disease, Group 3 (n = 71, mean age: 57 +/- 8 yrs) with multivessel disease. All the measured hemorheological parameters of IHD patients were significantly higher than those of controls. Fibrinogen and PV was significantly elevated in Group 2 and 3 comparing to Group 1 (p < 0.05 and 0.01). Hematocrit and WBV was significantly increased in Group 3 comparing to Group 1 and 2 (p < 0.05). CRI was significantly decreased in IHD patients, and it was also lower in Group 3 than in Group 2 (p < 0.05). These results indicate that hemorheological parameters may play a role in the pathogenesis and development of CAD.