The production of acute hypocalcemia was investigated using either 80 U. MRC of salmon calcitonin or 160 1. mrc of pork calcitonin in 117 subjects (58 patients with Paget's disease, 22 with osteoporosis, 22 with Sudeck-Leriche algodystrophy and 15 control subjects). The results obtained with the two types of calcitonin did not differ. Induced acute hypocalcemia was more pronounced in patients with Paget's disease than in the other subjects studied. In patients with Paget's disease there were statistically significant correlations between the hypocalcemia produced and the initial levels of alkaline phosphatase and total 24 hours urinary hydroxyproline.