The protein-synthesizing apparatus of sensitive neural cells was analysed in mature mammals at cultivation. Spinal cervical ganglia of mature rabbits were cultivated by the method of rotating tubes up to 4 days in a usual medium and in an amino-acid-enriched medium. The labelling level was defined radioautographically and by radioactivity of protein and acid-solving cell fractions registered by the scintillation methods. In order to obtain the fractions, Rose's method for dividing neural and glial cells in our modification was used. The glial neural cells were demonstated by our investigation to preserve their ability to incorporate the labelled leucine during any period of cultivation. The medium enriched with precursors of protein synthesis contributes to a more intensive incorporation of amino acid into protein and into the pool on the 4th day of cultivation, while the enriched medium sharply decreases radioactivity in the pool on the 1st day of cultivation. Intensity of the labelled leucine incorporation into the neurons drops towards the center of the explantat. The results obtained by the two methods coinside.