Cytochemical study of hepatocytes nuclei of the liver irradiated with a dose of 650 rad and irradiated after partial hepatectomy was performed. Morphological exponents of the intensive synthesis of preribosomal RNA in the nucleolus, as well as the transcription of heterogeneous RNA contained in perichromatin fibrils were revealed under the ionizing radiation effect. The behavior of perichromatin granules in the course of the experiment suggests delay in the transport of messenger RNA to cytoplasm, influenced by gamma radiation. Nuclear bodies were observed very often in nuclei of hepatocytes of irradiated animals.