Parathyroid hormone-related protein (PTHrP) is invoked as the cause of humoral hypercalcaemia of malignancy (HHM); it is contained in the keratinocyte layer of normal skin; and there is evidence that is is produced by fetal parathyroids. Antibodies against synthetic PTHrP peptides have been raised in rabbits and sheep. This immunohistochemical study has found that primary parathyroid adenomata and hyperplastic glands from patients with chronic renal failure stain positively with antisera against PTHrP(1-34) and PTHrP(50-69). Primary hyperplastic glands are negative. No staining with anti-PTHrP(106-141) antiserum could be detected immunohistochemically in any of the parathyroid adenomata or hyperplasia.