The activity of different formulations of synthetic calcitonins on the prevention of bone loss was evaluated in young women after oophorectomy. In the 1st study patients were treated or with salmon calcitonin (CTs) intramuscularly (100 I.U. every second day; 10 patients) either with CTs nasal spray (100 I.U. daily; 10 patients). In the 2nd study patients received or CTs i.m. (100 I.U. every second day; 10 patients) either a synthetic analogue of eel calcitonin (eCT) given i.m. (80 I.U. every 2nd day; 10 patients). All calcitonins formulations were given for 9 months with oral calcium supplement (1 g daily). In the 1st study no significant changes of bone mineral content (BMC) was found at the end of the treatment in both groups. In the 2nd study a statistically significant decrease of BMC was observed in the group treated with eCT while non relevant changes were found in the CTs treated patients. Slight side effects were observed in some patients treated with calcitonin formulations given i.m. Since salmon calcitonin nasal spray was well tolerated and prevented bone loss after oophorectomy its use might be recommended in the treatment of postmenopausal osteoporosis.