The author estimated the quantity of ammonia in the brain of the Rattus administered with such drugs as philopon, ritalin or meratran by Conway's diffusion analysis, and also the quantity of amino acids by the paperchromatography. The following are the results: 1. In the case of acute administration of philopon, the amount of ammonia in the Rattus brain increases markedly, while on the contrarily in the case of chronic administration it tends to decrease. Moreover, in the case of chronic administration all amino acids in the brain show a decreasing tendency. 2. In the case of acute administration of ritalin both ammonia and glutamic acid increase in the Rattus brain, whereas in the case of chronic adminstration the brain ammonia rather tends to decrease. 3. In the case of acute adminiattration of meratran, ammonia, glutamic acids, and aspartic acid all increase in the Rattus brain.