Hypophosphataemia is a common finding among kidney transplanted patients [1,2]. In a previous study in kidney transplanted children with plasma creatinine below 1.1mg/dl, we demonstrated [3] a negative correlation between plasma phosphorus and 1 alpha, 25-dihydroxyvitamin D3 (1,25(OH)2D3), the renal hormonal form of vitamin D. No such correlation was apparent in children with minimal increase in plasma creatinine. The aim of the present investigation carried out in hypophosphataemic transplanted adults was two-fold: 1) to determine whether hypophosphataemia results from persisting hyperparathyroidism or from a renal phosphorus leak, or both, and 2) to study the relation between plasma phosphorus, iPTH and 1,25(OH)2D3 in these patients.