The material for this experiment was brain tissues of normal rabbits whose cisterna magna had been previously injected with (32)P and obtained by decapitation after a fixed period of time. Decomposing phosphoric acids in the brain tissues into various fractions by Schneider's method, the author pursued the mode of (32)P migration in each fraction from the standpoint of time elements; and obtained the following results. Shortly after the injection (32)P is found to have migrated to acid-soluble fractions in the greatest amount but only little to other fractions. However, with lapse of time after the injection the rate of (32)P migration to the acid-soluble fractions decreases, especially markedly so to inorganic phosphoric acid fractions, whereas the rate of (32)P migration to phospholipid, nucleic acid, and phosphoprotein fractions gradually increases. Moreover, for a short period after (32)P injection the rate of (32)P migration to various fractions fluctuates markedly, but after 24 hours such a fluctuation in each fraction seems to diminish, apparently indicating a certain degree of stabilization.