Modifying effect of Solcoseryl upon the late postirradiation damage of the lungs expressed as the number of apoptotic cells per 1mm² of the pulmonary tissue was investigated in rats. The number of labelled apoptotic cells in situ was determined by TUNEL method under light microscope connected to computer imaging (Lucia software). The results of the experiment demonstrated statistically significant reduction in the number of apoptotic cells in the pulmonary tissue in the group of rats irradiated with simultaneous administration of Solcoseryl in comparison to the group of animals irradiated without Solcoseryl treatment. The results indicate that Solcoseryl exhibits radioprotective activity upon the respiratory epithelium due to the reduction of the apoptotic cell number.