The regional concentrations of intravenously injected 45Ca and total calcium were measured in rat brain during recovery from transient occlusion of the four major arteries to the brain. 45Ca was injected at intervals after ischemia, and the regional distribution of 45Ca was estimated by autoradiography. The 45Ca appeared to enter the brain via the choroid plexus, labeling the paraventricular tissue at 1 h after the injection. Control brains had more 45Ca in the gray matter compared to fiber-rich areas at 5 and 24 h, but within these regions the optical density was nearly uniform. The accumulation and retention of 45Ca in postischemic brain were selective and time-dependent. The regional pattern of 45Ca uptake correlated with the temporal progression of ischemic cell change. Infarction and preischemic hyperglycemia increased morphological damage, and increased the extent and distribution of 45Ca accumulation. The rise in total calcium concentration appeared to be biphasic in irreversibly damaged tissue.