Summary:Urinary adenosine‐3′, 5′‐cyclic monophosphate was measured in 14 patients with hypercalcaemia not caused by primary hyperparathyroidism. Increased levels were found in patients with malignant disease without bone metastases and believed to be examples of paraendocrine syndrome. Decreased levels were found in patients with meta‐static carcinoma involving bone, and in patients with multiple myeloma, lymphoma and immobilisation after fracture. Results obtained during treatment for hypercalcaemia are described in three patients.In two hypercalcaemic patients (one with hyperthyroidism and one with breast cancer with bone metastases) normal levels were found.This measurement is a useful substitute for assay of serum parathyroid hormone and is of value in the diagnosis of hypercalcaemia, in monitoring effects of treatment and in revealing underlying m