An ultrastructural study of ciliated epithelial cells in the ductuli efferentes of young and adult hamsters has revealed that these cells possess dense granules, dense granule clusters, dense bodies and fibrogranular complexes as reservoirs or precursors for ciliogenesis. The dense granules are first seen in the centrosomal region. Later, many dense granules and dense granule clusters appear in the apical portion of the epithelial cells where, subsequently, dense bodies are also found. Finally, the fibrogranular complexes are formed in adults. Morphological evidence strongly suggests that cilia are formed from diplosomal centrioles, de novo centrioles, dense body centrioles, and fibrogranular complex centrioles. Ciliogenesis begins in the fourth day after birth and increases rapidly in the fifth day. After the sixth day, cilia appear to be generated mostly from dense bodies and the total ciliogenesis activities gradually decrease as the animal ages.