The aim of the study was to ascertain the importance of calcitonin in the etiopathogenesis of osteoporosis in rats as an animal model. We used 20 female rats on which a thyroidectomy was performed, producing a calcitonin deficit. An autologous transplant of parathyroid gland and replacement therapy of thyroid hormone was carried out. The control group consisted of 20 rats. The levels of parathormone (PTH), calcitonin (CT), osteocalcin (GLA), seric calcium, and density, weight, quantity and mineral bone content of the head of the femur were measured. We found low levels of CT and normal amount of PTH, which contradicted the expected, there was an increment of the mineral bone content, without significant density, quantity and weight changes. We comment on these results.