Parathyroid hormone-like bioactivity in a patient with severe osteitis fibrosa cystica due to malignancy: renotropic actions of a tumour extract as assessed by cytochemical bioassay.

A patient is described with malignancy, hypercalcaemia and radiological evidence of severe parathyroid bone disease but undetectable concentrations of circulating immunoreactive PTH. Autopsy showed the tumour to be a metastatic bronchial carcinoid with no evidence of primary parathyroid disease. Extracts of the tumour had no PTH immunoreactivity but had high concentrations of a substance with identical activity to PTH in a cytochemical bioassay. The biological activity of the extract was not inhibited by PTH antibodies but was inhibited by an antagonist to PTH bioactivity.