1. A very large single dose of parathormone produced rapid and extensive decalcification of the bones of a young rabbit.
2. Gradually increased doses of parathormone failed to produce significant changes in the bones of young and fully grown adult rabbits.
3. Ammonium chloride, administered by stomach tube was without effect on the bones, when given to rabbits treated with parathormone or to otherwise untreated rabbits.
4. Calcium lactate did not promote the appearance of signs of parathormone overdosage in rabbits during treatment, nor were metastatic calcifications observed in the soft tissues after termination of the experiment.
5. The rabbit is relatively very resistant to the decalcifying effects of gradually increased repeated doses of parathormone, and therefore is not satisfactory material for experimental studies of bone changes of chronic hyperparathyroidism.
6. The appearance of actively transforming bones of a young growing rabbit, particularly at the sites of rapid growth, is not to be confused with the more severe fibrous processes produced by parathormone in guinea pigs, dogs and rats.