The distribution of labelled proteins in the brain after the injection of tritiated proline into the third ventricle was studied after autoradiography. In discrete areas, the incorporation proceeds at a faster rate after an avoidance training. The difference between trained and resting animals is much more evident after the injection of 100 units of L-Asparaginase. It is suggested that L-Asparaginase impairs long-term memory through the inhibition of protein synthesis.