The present study was undertaken to examine whether there is any hereditary correlation, with reference to the abnormal glucose metabolism, between patients with cerebrovascular accidents and their healthy blood relatives in respect to the occurrence of cerebrovascular disease. The investigation was carried out by intravenous glucose tolerance test (IV-GTT) and prednisolone-primed glucose tolerance test (PP-GTT) in 83 subjects. Of these, 20 were healthy (control) persons (group A), matched in age and sex with 50 patients with cerebrovascular accidents (group B) and 13 family relatives of group B (group C) showing unequivocal GTT or PP-GTT. In controls, the IV-GTT criterion, i.e. k value, was found generally to be 2.82 ± 0.43 and in persons less than 50 and over 50 years old, it was found to be related with age, i.e. 3.1 ± 0.73 and 2.53 ± 0.43, respectively. The 21 patients of group B with normal GTT response had a k value of 2.53 ± 1.88 and the 29 patients with abnormal GTT response had a k value of 1.2 ± 0.33. Among the 21 patients of group B, 11 had normal IV-GTT and their PP-GTT was found to be 125 ± 12.5 mg%. The other 10 patients with abnormal IV-GTT exhibited a PP-GTT of 173.4 ± 26.43 mg%. In 14 and 15 patients, the time-lapse difference of 7 and 8-21 days after stroke showed an abnormal GTT response and in 6 and 15 patients it showed a normal response. Among 13 healthy relatives of group B (group C), only 1 subject was found to have abnormal IV-GTT (k value of 1.386) and 2 were found to have abnormal PP-GTT (182.8 and 388.0 mg%), thus indicating pre-symptomatic dia