AVAILABLE knowledge on the dipeptidase activity of brain is limited to the enzymatic hydrolysis of DL-alanyl-glycine1–3. Detailed studies by Pope et al. have dealt with the intralaminar distribution of dipeptidase activity towards DL-alanyl-glycine in the cerebral cortex of rat1,2 and man3. Our own studies on proteolytic activity of brain led to a systematic inquiry into the existence of any selective or preferential dipeptidase activity of brain towards any particular dipeptidase structure. The present preliminary report deals with the systematic quantitative differences observed in the hydrolysis of the series of N-glycyl-dipeptides by mouse brain.