1. Alcoholic extracts of testis, when injected into rabbits, produce a fall in blood calcium.
2. The character of the fall of the blood calcium is the same as that obtained after injection of ovarian extract, but the minimum dose required is about ten times as large as in the case of the ovary.
3. Extraction of the "crude" alcoholic extracts with ether does not give rise to an active fraction.
4. It is concluded that the drop of the blood calcium produced by the testicular injection is due to an internal secretion present in the testis.