Calcitonin (CT)-cells were detected, by using an anti-human calcitonin serum (hCT), in the thyroid of the normal and anencephalic human fetuses. The first CT-cells were observed at 14 weeks of gestation. The CT-cells were at first isolated afterwards were appeared in parafollicular localization. The CT-cells were only observed in the middle of the upper or medium third or the lateral lobes, along the central axis of the lobes. No CT-cells were detected in the isthmic region or in the inferior third of the lobes. CT-cells were also seen in the thyroid of the anencephalic fetuses. The specificity of the immunocytological reaction was ascertained after incubation of anti-hCT serum with homologous or heterologous antigens: after incubation  of the anti-hCT serum with hCT, the immunocytological reaction was disappeared, but no modification of the reaction was noted after incubation with somatostatin, T4 or parathormone. The CT appeared precociously in the thyroid of the human fetus and their localization was the same that in the older subjects.
Calcitonin Fetus