Hypercalcemia is a postrenal transplant complication. We found a high frequency of elevated plasma ionized calcium values (65.8%) in 41 normal-function renal graft recipients. In 8 patients increased free calcium was associated with high PTH levels, whereas in 19 PTH was not increased but free calcium was high. In the other 14 patients both free calcium and PTH were in the normal range. The mean transplant duration was different in the three groups: shorter in high PTH patients, longer in normal free calcium patients, intermediate in normal PTH and high free calcium patients. Our findings confirm that a condition of hyperparathyroidism persists in the first post-transplant period, and suggest that this complication evolves towards normalization of the blood chemistry values, passing through a condition of inappropriate PTH secretion with elevated plasma free calcium which in this period is the only marker of parathyroid hyperfunction.