The relationship between the type of operation for primary hyperparathyroidism and the incidence of postoperative hypocalcemia has not been completely elucidated. The pre- and postoperative serum calcium concentrations in 107 patients with this disease who were operated upon for the first time utilizing several different procedures were evaluated. Group 1. Prior to 1978, our aim was the excision of an adenoma, if present, and any other questionably enlarged parathyroid glands. All other appearing glands that could be found were biopsied. If parathyroid normal hyperplasia was present clinically, three and one-half glands were removed. Group 2. (1980 through 1981). A bilateral neck exploration was performed. If an adenoma was present, this was removed. However, only one or two other parathyroid glands were biopsied. The last normal appearing gland was intentionally left undisturbed. If hyperplasia was present, 2 glands were resected and remnants of two other glands were left in situ. Following their initial neck exploration, 52 of 57 (91%) Group 1 patients were cured. During the first 4 postoperative days, 48% had one or more serum calcium values of 7.9 mg/dl or lower (our criterion for significant postoperative hypocalcemia). None had permanent hypoparathyroidism, however. Their serum calcium concentrations fell to the same level whether one, two or three glands were excised. All 50 patients in Group 2 were cured by their initial neck exploration. Only 26% developed serum calcium values of 7.9 mg/dl or lower (p less than 0.05. when compared to Group 1). However, one patient who had the removal of a large substernal goiter and a parathyroid adenoma has manifested prolonged hypocalcemia. Our data demonstrate that by performing a more conservative operation, transient postoperative hypocalcemia can be lessened. Furthermore, it is quite suggestive that excessive parathyroid biopsy may be deleterious and should be avoided.