In a group of 22 patients with focal ischemia of the brain and in 11 patients with cerebral arteriosclerosis and vascular hypertension the tolerance to glucose administered by the i.v. route was investigated. The rate of glucose utilization was expressed by a utilization coefficient. The tolerance to i.v. glucose administration is reduced in the group of arteriosclerotic and hypertensive subjects. As a result of acute focal ischemia of the brain it declines even more, as compared with subjects in the control group. In the mean values of the coefficient of glucose utilization a significant difference was recorded between the group of patients with focal ischemia of the brain, as compared with the control group (p less than 0.001) and the group of arteriosclerotic and hypertonic patients, as compared with controls (p less than 0.005). The authors conclude from the results that the reduced glucose tolerance to orally administered glucose in patients with focal ischemia of the brain and their potential candidates in no causal relationship with the variability of intestinal absorption, as similar changes in glucose tolerance were recorded also after intravenous administration.