The study takes up the problem whether synthesis of certain protein fractions in nerve cells of the hippocampus in rats during the transfer of handedness may be specific for this learning process. Electrophoretic separation of protein was carried out on polyacrylamide gels at the microscale. The investigation encompasses the brain-specific, acidic protein S100 and two protein fractions moving close to the S100 protein during electrophoresis. The protein synthesis was studied during one month of intermittent training of the animals. The temporal link between behavior and an increase in the synthesis of nerve-cell protein indicates that the protein response is specific for the processes occurring in the hippocampus during learning.