A case of pseudohypoparathyroidism has been investigated. Indirect evidence allows to eliminate a defect of renal 1 alpha-hydroxylase as the determining factor of this condition. Similarly, the increased size of the mean surface area of the cross-section of periosteocytic lacunae, as determined on decalcified sections of bone obtained by transiliac biopsy, shows the osteocytes to be sensitive to the endogenous PTH, discarding cAMP response to PTH in bone as a prerequisite for PTH action on bone. The authors conclude from these data and from previous experiments that the defect of parathyroid function in this condition probably relates to the existence of an abnormal PTH molecule and/or metabolism and/or interaction with the receptors sites. The endocrine function was studied as well. Prediabetes was demonstrated, as well as primary latent hypothyroidism (TRH test). Prolactin release could not be stimulated by TRH, levodopa, metoclopramide, chlorpromazine and insulin hypoglycemia. The latter produced a normal release of ACTH (as ascertained by plasma cortisol levels) and GH, and possibly a sluggish response of glucagon and gastrin. There was a deficiency of urinary concentration upon restriction of fluid intake. This was only partially corrected by ADH administration.