Serum parathyroid hormone (PTH) levels in 6 patients who had received parathyroid tissue autografts were studied. Samples were taken from graft and non-graft arms both pre- and post-dialysis. Each sample was analysed using two PTH assays, one measuring C-terminal PTH and the other measuring the intact PTH molecule. For both pre- and post-dialysis samples an appreciably greater difference was seen between the graft and non-graft arms using the intact assay. A patient with suspected ectopic PTH production showed a very much reduced differential between the two sampling sites with both assays. We suggest that the intact PTH assay is of greater clinical utility in the localisation of ectopic glands and monitoring of graft function than the commonly used C-terminal assays.