For the purpose to find the exact position of neonatal line in Japanese, ground sections of 475 human deciduous teeth were examined histologically. Obtained results are as follows.
1. The position of neonatal line was not characteristic and showed considerable variation in each tooth type, especially on the anterior teeth.
2. The variation of position would be mainly owing to the change of physiologic condion of new- erine period or of the gravity at birth. The considerable variation on the anterior teeth would be ow ng to the constitutional feature of their enamel.
3. The position of neonatal line in Japanese had a trend to appear at incisal or cuspal portion of the tooth crown than the position in American or European people.
4. Toot development in female showed a tendency more earlier than in male at birth-time.
5. The tooth development of the children born after 1950 at birth was thought more fast than of the born at The War-Time and the soon after, but the further investigation about this result will be done.