To investigate the pathogenesis of post-thyroidectomy hypocalcemia calcium, phosphate, calcitonin, parathormone, albumin, triiodothyronine and thyroxine levels were monitored during operation and postoperatively in 25 female patients undergoing bilateral subtotal thyroidectomy for non-toxic nodular goiter. A highly significant fall in uncorrected serum calcium and albumin levels started with the completion of lobectomies and a significant correlation between the course of serum calcium and albumin levels were seen, an early peak in calcitonin corresponded well with the a drop in corrected calcium and inorganic phosphate levels. An overt parathyroid response to hypocalcemia was not observed. We conclude, on the basis of the postoperative hypoalbuminemia, that a calcitonin leak triggered the early onset of hypocalcemia while an insufficient parathyroid response contributed to the post-thyroidectomy hypocalcemia.