1. After thyroidectomy with partial parathyroidectomy the maximum and average hemolytic titers of the sera of rabbits injected intravenously with sheep blood are equal to or higher than those of normal animals similarly injected.
2. Thyroidectomy with partial parathyroidectomy does not inhibit antibody production. This fact is in accord with the results of Garibaldi, Launoy and Lévy-Bruhl, Lerda and Diez, and others.
3. Thyroidectomy with partial parathyroidectomy does not cause serious disturbance in the adult rabbit. If the operation is performed properly, the animals survive and only moderate cachexia develops in time.
4. After complete thyroparathyroidectomy a small proportion of the animals survive even after developing very severe tetany. Those that recover do not show further signs of serious disturbance, but in time develop a moderate degree of cachexia no greater than that of the thyroidectomized animals.
5. Thyroparathyroidectomized rabbits develop anti-sheep hemolysin of a uniformly low titer—on an average one-fifth that of the controls.
6. Injection of bovine blood into rabbits that survived complete thyroparathyroidectomy from 1 to 2 months previously results in the production of hemolysin of a uniformly low titer compared with that of normal animals similarly treated.