Blood rheologic parameters were examined in 16 patients without multiple organ failure 2 weeks after coronary artery surgery. The whole blood viscosity (shear rate = 94.5 sec-1) was unchanged (4.59 +/- 0.53 to 4.56 +/- 0.58 mPa.s) despite a significant decrease in hematocrit (39.8 +/- 4.3 to 37.1 +/- 3.8%, P less than 0.05). The oxygen delivery index (the ratio of hematocrit to whole blood viscosity) was significantly decreased (8.67 +/- 0.35 to 8.18 +/- 0.59%/mPa.s, P less than 0.05). Plasma viscosity (shear rate = 94.5 sec-1) increased significantly (1.60 +/- 0.13 to 1.72 +/- 0.10 mPa.s, P less than 0.01), as did serum levels of globulin (2.8 +/- 0.4 to 3.0 +/- 0.4 g/dl, P less than 0.01), alpha 1-antitrypsin (232 +/- 41 to 308 +/- 60 mg/dl, P less than 0.001), and fibrinogen (381 +/- 81 to 479 +/- 117 mg/dl, P less than 0.001). Total protein and globulin levels showed a good correlation with plasma viscosity, but the fibrinogen concentration demonstrated no correlation. The passage time of a 40% red blood cell suspension (0.5 ml) was shortened significantly from 10.2 +/- 1.1 to 9.2 +/- 1.0 sec (P less than 0.05). These results indicate that an increase in plasma viscosity is important in determining blood rheologic properties 2 weeks after coronary artery surgery.