Electron microscopy and morphometry of neurons in layer V of the somatosensory area in the neocortex and CA3 field in the dorsal hippocampus showed that single and 5-fold intraperitoneal injection of Polidan was followed by ultrastructural and metabolic changes in neurons reflecting activation of protein synthesis. The number of free ribosomes decreased; the number of polysomes and count of ribosomes in polysomes and tubules of the granular endoplasmic reticulum increased. Study of mitochondria and neuropil showed that Polidan activates synthetic processes in the neocortex and hippocampus. It should be emphasized that single treatment with Polidan led to functional activation of synthetic processes, while 5-fold injection of Polidan was followed by hyperactivation of synthetic processes and depletion of ultrastructures in the neocortex and hippocampus.