The ultrastructure of odontoblasts of deciduous teeth from two human fetuses (CRL 159 and 195 mm) was investigated. The human odontoblast is a polarized cell with a characteristic localization of its organelles and demonstrates similarities with odontoblasts from non-human materials. Vesicular and granular elements were found to be formed in the Golgi complex, and these elements were also observed in the odontoblastic process, thereby indicating a secretory process. No special organization of the predentinal collagen fibrils was observed. In the newly formed dentin a thin sheath of non-mineralized material was seen to surround the odontoblastic process. The ultrastructural findings are correlated to the findings of recent histochemical investigations.