The interventional group will consist of 11 patients scheduled for elective parathyroidectomy who will receive MB infusion (5mg.kg-1 in 250 ml 5% glucose-saline) approximately 60 min before anaesthesia induction. A further 11 patients scheduled for unilateral thyroid lobectomy without MB pre-treatment will be recruited as controls. They will present with normal thyroid tests and will carefully be selected in an attempt to match the intervention group on the basis of age, weight and sex. Both types of surgical procedures will be performed by the same surgical team.