Leptin, a 16 kDa non-glycolated polypeptide of 146 amino acids produced by the ob gene, has a variety of physiological roles not only in lipid metabolism, hematopoiesis, thermogenesis and ovarian function, but also in angiogenesis. This study focuses to investigate the possibility that leptin, as an angiogenic factor, may regulate the angiogenesis during tooth development. We firstly studied the expression of leptin and vascular endothelial growth factor (VEGF) during tooth development immunohistochemically. This investigation revealed that leptin is expressed in ameloblasts, odontoblasts, dental papilla cells and stratum intermedium cells. This expression pattern was similar to that of VEGF, one of the most potent angiogenic factors. Interestingly, more leptin-positive cells were observed in the upper third portion of dental papilla, which is closest to odontoblastic layer, compared to middle and lower thirds. Moreover, in the dental papilla, more CD31 and/or CD34-positive vascular endothelial cells were observed in the vicinity of ameloblasts and odontoblasts expressing leptin and VEGF. These findings strongly suggest that ameloblasts, odontoblasts and dental papilla cells induce the angiogenesis in tooth germs by secretion of leptin as well as VEGF.