R O u t c r w his article reviews the experience at our institution ith infusion of methylene blue during parathyroidctomy and subsequent development of a rare enephalopathy. Use of methylene blue for localization f parathyroid adenomas is a well-described and timeroved technique. Its use aids identification and can ecrease operative time. Few complications have ever een noted. There are only four case reports within he literature of neurologic sequelae after administraion of methylene blue. Over the past 6 years, we have erformed 132 parathyroidectomies aided by ethylene-blue infusion, with unexplained encephaopathy developing in 5 patients. Interestingly, all the atients in whom encephalopathy developed had conurrent use of medications that altered the metabolism f serotonin. The same proved true for the patients in he four previous case reports, although no association ad been made, as they appeared as isolated cases. In our eries, encephalopathy did not develop in any patient ithout concurrent use of serotonin reuptake inhibitors. his proved significant when analyzed using Fisher’s exct test (two-sided p 0.00002). We believe that use of ethylene blue in patients currently taking drugs that lter the metabolism of serotonin should be reconsidred, as this can cause a profound and potentially lifehreatening encephalopathy. Methylene blue is an interesting compound, used or over 100 years to treat a variety of afflictions. Its roperties as a dye, electron transport agent, antisepic, pressor, photosensitizer, and psychotrope have led o its broad use for many applications. Its most ommon modern medical application is as an antiote for methemoglobinemia. Methylene blue is frequently used in surgical practice or localization of parathyroid adenomas. Its use aids dentification and can decrease operative time. The dye