A 1-min calcium injection was compared with a pentagastrin injection as provocative measures in stimulating calcitonin secretion in 4 patients with medullary thyroid carcinoma. In all cases the calcium injection resulted in a greater rise in serum calcitonin concentration. The patients tolerated the calcium injection well. However, two patients experienced substernal pressure and dyspnea following the pentagastrin injection. It is concluded that a 1-min calcium injection is a safe, rapid and effective procedure in the diagnosis of medullary thyroid carcinoma.