Forty-three patients were treated for a total duration of 301 patient-years with calcitonin (CT) (range 3-16 years, median duration 6 years 6 months). Eighty-four percent of patients were suffering from complications associated with Paget's disease and the remainder from osteoporosis. In the majority of patients, CT was administered by the subcutaneous route and one patient was psychologically dependent on calcitonin injections. There were no long-term side effects associated with CT therapy. In a separate group of 105 patients consisting of 83 patients on human CT and 22 patients on salmon CT, injections showed short-term side effects in 77% and 64% of these patients, respectively (NS). Side effects associated with nasally administered salmon CT in 25 patients were mild and of low incidence (32%). Long-term administration of calcitonin in humans is safe and devoid of any serious or long-term side effects.