1. Acceleration of the metamorphosis of frog tadpoles is induced by injections of commercial extracts of the anterior lobe pituitary gland extract.

2. The acceleration of metamorphosis produced by iodine in solution in suitable concentrations is not so great as that produced by injections of the anterior pituitary extract.

3. Further increase in the acceleration occurs when the injected specimens are kept in suitable concentrations of iodine solution.

4. The sequence of changes is similar to that observed in the accelerated transformation of tadpoles produced by thyroid or iodine diet.

5. The highest mortality, greatest reduction in size, and most rapid transformation occurs in the highest concentration of iodine, and this is still greater in injected animals kept in iodine solutions.

6. The younger the tadpole the less chance is there of completing metamorphosis under the accelerating stimulus of injected anterior lobe or iodine.

7. There is a paling effect after initial injection less marked in older specimens which is possibly due to inhibiting influence on the posterior lobe of excess of anterior lobe secretion. Idoine has no definite pigment action.

8. Iodine appears to act independently of the anterior lobe injection in the tadpole, the acceleration being apparently the sum of their separate actions.

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