My colleagues and I thank Drs Ryan and Dwarakanathan for sharing their experience with sclerosing thyroid cysts with us. We are pleased that they have found the technique using tetracycline to be "salutary." The observation of an acute pain response to the instillation of tetracycline in two patients is of interest and is similar to the response observed in one of our subsequent patients who likewise had no long-term untoward effects. We agree that the cause of the pain is probably extravasation of the sclerosing solution into the surrounding tissues with subsequent irritation of sensory neural tissue. We also agree that to avoid extravasation the cyst should be only partially evacuated, a maneuver that helps to maintain the needle tip in the cyst cavity during the instillation procedure. The suggestion to mix local anesthetic with the sclerosing agent is intriguing and would be expected to diminish the occasional painful response