Pigeons were divided into two numerically equal groups (A and B) containing 30 specimens each. Birds from group A were intraperitoneally injected daily with 0.1 mL/100 g body wt of vehicle (0.1 M acetate buffer, pH 4.3 containing 0.1% gelatin). Specimens from group B were intraperitoneally injected daily with 1 microg/100 g body wt of salmon calcitonin. Six birds were sacrificed from each group 2 h after the last injection on 1st, 3rd, 5th, 10th, and 15th day of the experiment. After collection of blood samples, ultimobranchial and parathyroid glands were fixed for histological studies. In calcitonin-treated C. livia, the plasma calcium levels exhibit a progressive decline from day 1 till day 5. On day 15, the levels become more or less similar to the control value. No change has been noticed on day 1 in the plasma phosphate levels of calcitonin-treated C. livia. The levels decrease progressively from day 3 to day 5; thereafter, it exhibits an elevation so that on day 15, normal plasma phosphate levels is achieved. The ultimobranchial gland of C. livia exhibits no change up to day 5 following calcitonin treatment. The nuclear volume of ultimobranchial cells exhibits a decrease on day 10. This response progresses up to day 15. Few degenerating cells are also discerned following 15 days calcitonin treatment. The parathyroid gland of calcitonin-treated C. livia exhibits no histological alteration up to day 3. The nuclear volume of parathyroidal cells exhibits a progressive increase from day 3 till the close of the experiment (day 15). Moreover, the gland exhibits more compactness on day 10 and day 15. Few degenerating cells are encountered after day 15 following calcitonin treatment.