ExtractAn intravenous injection of 100 units of thyrocalcitonin was given after an 18-hour fast to seven normal children and seven children with hypothyroidism. The effect on levels of calcium in blood was measured 1, 2, 4, 6 and 24 hours after injection. Among the normal children, the average decrease in levels of calcium in mg/1 was 1 h, 7.70 ± 3.08; 2 h, 5.40 ± 2.82; 4 h, 2.30 ± 2.85; 6 h, 1.30 ± 2.24; 24 h, 1.40 ± 2.35. In the hypothyroid children (5 with athyreosis and 2 with thyroid dysgenesis) the decrease was 1 h, 9.40 ± 2.52; 2 h, 10.50 ± 2.17; 4 h, 9.40 ± 2.29; 6 h, 8.10 ± 2.54; 24 h, 2.00 ± 3.22. In comparison with the normal children, the hypocalcemia in the hypothyroid children was greater and more prolonged.SpeculationThe hypocalcemic effect of the thyrocalcitonin is more important for the child than for the adult. This fact is no doubt related to the mechanism of the hypocalcemic action of the thyrocalcitonin, which is the inhibition of the osseous catabolism. The release of thyrocalcitonin causes an imbalance in calcium metabolism, which results in a hypocalcemia more marked in the normal child than in the adult, and in the hypothyroid than in the normal child.