The causes of temporary hypocalcemia after thyroidectomy are not well understood. In 18 patients undergoing unilateral (UL) and bilateral thyroid lobectomy (BL), an attempt was made to preserve all parathyroid glands with an intact blood supply. Total calcium (bound and free), free calcium (physiologically active form), albumin, parathyroid hormone, and calcitonin levels were serially measured. After UL, free calcium, parathyroid hormone, and calcitonin levels were unchanged, but total calcium level decreased because albumin level decreased. After BL, total calcium level decreased due to a decrease in albumin-bound calcium level. Free calcium level also decreased due to a decrease in parathyroid hormone level. Calcitonin level did not change. Despite careful preservation of the parathyroids and their blood supply, BL is frequently associated with temporary hypoparathyroidism. Techniques for preservation of parathyroid glands with their vascular integrity, correlation of surgical manipulation of parathyroids and calcium level, and calcium binding are discussed.