An adult woman with pseudopseudohypoparathyroidism had a child with normal calcium and parathyroid hormone concentrations and cyclic AMP response to injected parathyroid hormone in infancy. By 2.5 years he had features of pseudohypoparathyroidism with raised parathyroid hormone and 'flat' cyclic AMP response. This is the first documented case of a change in parathyroid hormone responsiveness. The abnormal cyclic AMP response to parathyroid hormone in pseudohypoparathyroidism can evolve during childhood.