In 40 patients suffering from chronic ischemic heart disease (16 with history of myocardial infarction, 10 with unstable angina and 14 with stable angina) and in an equal number of sex-and age-matched control subjects, we have determined plasma and blood viscosity according to RAND et al. using a Wells-Brookfield Micro-Viscometer, shear rate 230 sec-1, and red cell filterability according to REID et al. Significant differences were found in patients suffering from ischemic heart disease, in comparison with the control group, for blood viscosity (p less than 0.01), plasma viscosity (p less than 0.001) and red cell filterability (p less than 0.001). The changes of hemorheological parameters in ischemic heart disease, especially in patients suffering from unstable angina and in those with history of myocardial infarction, point to the opportunity of a pharmacological treatment aiming at improving the district microcirculation.