Intraoperative staining of parathyroid glands with methylene blue was used in 120 cervical explorations for hyperparathyroidism. The dye clearly stained 66 of 67 adenomas (98%) and 194 of 198 hyperplastic glands (98%). No recurrences were observed in 66 patients undergoing surgery for an adenoma. Six of 48 patients (12%) had recurrences of hyperplasia of the parathyroid glands. We found methylene blue to be an effective, safe, and easy applicable method to quickly identify abnormal parathyroid glands, thereby considerably shortening the operating time.