Thallium-Technetium isotope subtraction scanning was used routinely as a preoperative localization investigation in 90 patients with primary hyperparathyroidism who were submitted to "first-time" cervical exploration from 1985 to 1988. When the scintigram demonstrated a single focus of activity suggesting the site of a solitary parathyroid adenoma, a scan-directed exploration was carried out. If the tumor was found at the location suggested by the scan, it was then removed and the ipsilateral normal parathyroid was biopsied. The contralateral side of the neck was not explored in these patients. A total of 48 patients underwent unilateral cervical exploration while the remaining 42 individuals had a standard bilateral neck operation performed. The difference in operating times for patients who had a solitary adenoma and who underwent unilateral and bilateral neck exploration, respectively, was statistically highly significant (71 minutes versus 97 minutes, p less than 0.001). At mean follow-up of 16.8 months, no patient who had a unilateral neck exploration performed for solitary parathyroid adenoma demonstrated persistent or recurrent hypercalcemia.