We have examined the development of rat striatum for evidence of cells dying in the process of physiological cell death. In present study we have indicated apoptotic cells in sections stained with cresyl violet (cell death characterized by pyknosis) or with DNA end labeling assay (TUNEL method). Our results demonstrated that cell loss during maturation of the rat striatum had the characteristics of apoptosis rather than necrosis. The greatest number of TUNEL - positive and pyknotic cells in the striatum were found during the first postnatal days; after 7th day of postnatal life a rapid decrease of its number was observed. After the second postnatal week no TUNEL-positive cells were observed in the striatum. Our analysis suggests that apoptotic cell death occurring during the development of striatal neuronal population takes place during the first week of postnatal life.