Human calcitonin (hCT) response to a 1-minute calcium infusion was studied in 6 male and 4 female young normal subjects and in 6 male and 6 female elderly subjects. In the young subjects plasma hCT levels increased significantly (p less than 0.01) from mean basal value of 82.3 +/- 48.7 pg/ml to maximum level of 407.5 +/-198.0 pg/ml in the male, while it increased from 96.3 +/- 89.2 to 216.3 +/- 89.1 pg/ml p less than 0.05) in the female. In the elderly subjects, it increased from 80.3 +/- 56.9 pg/ml to maximum level of 229.2 +/- 130.6 pg/ml (p less than 0.05) in the male, while it increased from 109.2 +/- 43.7 to 163.3 +/- 55.7 pg/ml (p less than 0.005) in the female. There was no significant difference in the basal hCT level of these 4 groups. In both the young and the elderly, however, mean increment of hCT level was significantly (p less than 0.05) higher in the male than in the female of the same-aged group. In both the female and the male subjects, it was significantly (p less than 0.05) higher in the young than in the elderly of the same sex. A 1-minute infusion of calcium can be used as a reliable provocative test for hCT secretion in human subjects.