A study has been undertaken to document in detail some of the changes that occur following parathyroidectomy in chronic renal failure patients. In an attempt to predict more precisely the timing of the post-operative hypocalcaemia, serum parathyroid hormone (PTH) concentrations were measured in six patients with renal osteodystrophy undergoing subtotal parathyroidectomy [5] and total parathyroidectomy [1]. The values obtained were related to post-operative changes in serum calcium and albumin concentrations. The intact-PTH concentration in serum was shown to decline rapidly post-operatively while the C-terminal PTH followed a more gradual course. Neither total nor ionised serum calcium concentrations exhibited a correspondingly dramatic fall after parathyroidectomy and the serum albumin concentration remained unaltered.