Basically I agree with all the points raised by Dr. Butler. We believe that the patient referred to by him and patients with infantile vitamin D deficiency rickets are similar in that all develop secondary hyperparathyroidism as a result of deficient calcium absorption from the bowel. Furthermore both types of patients appear on occasion to reach a state when they do not show a tissue response to administered parathyroid hormone. This may occur at varying serum calcium levels (personal unpublished data) which implies that failure to respond to endogenous parathyroid hormone also occurs.