1. Administration of CoCI2 induces a discontinuous three-phase hyperglycernia in the snake (n. Natrix natrix). 2. Initial hypcrglycemia seems to be of adrenalinic origin, a fact demonstrated by treatment with ergotamine and reserpine resulting in no or only a negligible hyperglycemia, respectively. 3. The decrease of hyperglycernia in the interval from 6 to 9 hours is due to a hyperinsulinemia of B-pancreatic origin, a result of the property of Co of crystallizing insulin. This fact is evidenced electron microscopically by the growth of the relationship between crystallized and non-crystallized granules. 4. Finally, compensatory hyperglycemia IS ot A2-pancreauc origin, illustrated both by increased secretion indices of A2 ceHs, such as partial degranulation of the cells, as weH as by increased proteinic synthesis indices, Le. ergastoplasm development, a multitude of ribosomes, occurrence of granules of smaH dimensions.