Alkaline phosphatase was studied in an inpatient series of geriatric admissions aged sixty and over. Bone disease, particularly bone trauma, metastases, Paget's disease and osteomalacia, was the major cause of elevation but liver disease and rheumatoid arthritis were also important. Skin ulceration over bone and osteoarthritis may possibly be causes of slight elevation of alkaline phosphatase. After removal of patients with relevant diagnoses, a ‘normal’ group of 259 patients remained from which an upper limit of 12·8 King-Armstrong units for the elderly was obtained. There was no correlation with age or sex and it is suggested that positive correlation with age and higher values in the elderly female reported by other authors may be due particularly to the inclusion of unrecognized cases of osteomalacia and Paget's disease.