In pseudohypoparathyroidism there is a resistance to the action of the parathormone in its target organs. Patients with this disease show clinical and laboratory data of hypoparathyroidism with normal or high levels of parathormone. Three types of pseudohypoparathyroidism are known according to the site in which the disorder is localized, within the complex formed by the cell receptor for the hormone and the adenylate cyclase systems of the cell membrane: Ia, Ib and II. The response of plasmatic and urinary cyclic AMP to the administration of parathyroid hormone may be useful to establish the type of pseudohypoparathyroidism presented in determined patients. Three cases of pseudohypoparathyroidism in whom an intravenous stimulation test with the synthetic 1-34 fragment of the human parathormone [teriparatid acetate (PARATHAR)] are presented. These patients were diagnosed according to the responses of cyclic AMP of type I pseudohypoparathyroidism. The methodology followed for the study and the results obtained are commented.