Humoral hypercalcaemia of malignancy: report of two further patients with biochemical studies on tumour extracts.

1. Tumour extracts from two patients with humoral hypercalcaemia of malignancy contained material which stimulated adenylate cyclase in chick renal membranes and in rat osteosarcoma cells. 2. Adenylate cyclase-stimulating activity in each system was inhibited by a specific parathyroid hormone (PTH) antagonist. 3. Studies in two HPLC systems suggested that the adenylate cyclase-stimulating factors extracted from these tumours differed from each other and from synthetic human parathyroid hormone 1–34. 4. The presence of similar PTH-like adenylate cyclase stimulating material(s) in oncogenic osteomalacia suggests that adenylate cyclase stimulating factor(s) may not be the direct or the sole cause of hypercalcaemia.