We studied the incorporation of P(32) into the mucoprotein (M. P.) in rat's brain, and obtained the following results 1). The M. P. content and the counts measured with Geiger Mueller's Counter increased under the influences of radioactivity until the fourth day after P(32) injection. 2). The M. P. in healthy rat's brain showed just similar to lecithin a slow turnover. 3). In comparison with control, the M. P. content in rat's brain receiving electroshock convulsion gave rise to marked increase and acceleration of its turnover. 4). The M. P. content in rat's brain submitted to insulinshock treatment decreased, but its turnover accelerated about the ninth day.