1. An adenylate cyclase bioassay for parathyroid hormone (PTH) was evaluated in peripheral sera of ten normal subjects, 15 patients with various types of hypoparathyroidism, nine patients with malignancy-associated hypercalcaemia and 60 patients with primary or secondary hyperparathyroidism. The lower limit of detectability was 150 pg/ml in terms of synthetic human PTH (1-34).
2. PTH-like bioactivity was not detected in normal subjects, in patients with surgical hypoparathyroidism, in patients with idiopathic hypoparathyroidism or in patients with malignancy-associated hypercalcaemia. Serum from one untreated pseudohypoparathyroid patient consistently contained PTH-like bioactivity.
3. Bioactivity was detected in sera from 50% of patients with primary or secondary hyperparathyroidism. In two patients with secondary hyperparathyroidism calcium infusions suppressed this activity within 5 min.
4. Both in primary and in secondary hyperparathyroidism there was a significant positive correlation between levels of PTH-like bioactivity, PTH immunoreactivity and the histological severity of the disease.