In this paper we present the results of a 12-month double-blind clinical multicenter study assessing the effects of synthetic salmon calcitonin (CT) administration in a group of white postmenopausal osteoporotic women. Treated patients were given 100 MRC units of synthetic salmon CT injected i.m. in the morning every other day. Control patients received a placebo injection. All patients received 500 mg of elementary calcium p.o., b.i.d. Bone mineral content (BMC) was measured at the extreme distal radius of the nondominant arm by a dual photon bone densitometer which utilizes two radionuclides, 241Am and 125I, with energies of about 60 keV and 30 keV respectively. Biochemical parameters of calcium-phosphorus metabolism were also measured. After 12 months of treatment a significant mean increment of BMC and nondialyzable OHPr/creatinine values and a significant decrease of total OHPr/creatinine values were observed in the treated group, while controls showed a significant decrease in BMC values. These results, together with the observation that in some patients the decrease in total OHPr/creatinine values was not accompanied by an increment of BMC, show that long-term salmon CT treatment may be of benefit in postmenopausal osteoporosis and that the effects of CT on bone mass may be due not only to the inhibition of bone resorption but also to the stimulation of bone formation.