1. Detailed observations on the effect of growth hormone upon rabbbit dentine revealed that it had, both quantitatively and qualitatively, accelerative effect upon the growth and calcification of dentine. In this case, the stripe figure, produced by calcification of baily cycle, remained unextinguished.
2. Anterior pituitary preparations-Hypohorin, Ploran, Prae-hormon and ACTH-also demonstrated some calcification/accelerating effect, though with some differences between them and f rom that of growth hormone.
3. Atonine, a posterior pituitary preparation, did not show so evident effect, but Pituitan showed inhibitory effect on calcification of rabbit dentine. The posterior lobe did not seem to bear on the acceleration of growth of teeth.
4. Extract from the cattle pituitary gland demonstrated especially remarkable accelerative effect on calcification of dentine. When the action of the pituitary gland upon calcification is discussed, it may be necessary to consider not only the calcification-accelerating effect of growth hormone but also action of ACTH and moreover that of the pituitary-adrenal axis.