The values of BV at tangential velocity (TV) 10sec^-1, 20 sec^-1, 40 sec^-1, 100 sec^-1, and the values of plasma viscosity (PV) at TV 100sec^-1in 215 cases of healthy adult, and also in 52 cases of diabetes, 135 cases of cerebral infarction, 26 cases of cerebral apoplexy, 92 cases of pulmonary heart disease and 58 cases of coronary heart disease had been measured. The results showed that in above mentioned diseases the viscosity at four kinds of TV was evidently increased, especially at low TV. It was one of the most important mechanisms in these diseases that increase of BV and erythrocyte aggregability leaded to microcircular disturbance and reduction of perfusion of tissues. The results provided that MBV was great helpful in studying effective prevention and treatment of microcircular disturbance, also it was helpful in differential diagnosis of cerebral infarction and apoplexy.