Horace Wells, a dentist in Hartford, Connecticut, first used nitrous oxide in dentistry in December 1844. A few weeks later he travelled to Boston, Massachusetts, to demonstrate to physicians and dentists the use of nitrous oxide in painful procedures. Wells’ unsuccessful demonstration of nitrous oxide for the extraction of a tooth is well known, but other details of this trip are poorly understood. A description of Wells’ visit to Boston was compiled using information from 21 statements and 5 newspaper notices. The precise date and location of Wells’ demonstration could not be determined. There is no primary evidence that Wells’ demonstration occurred in the surgical amphitheater (Ether Dome) at Massachusetts General Hospital. Wells’ demonstration of nitrous oxide probably occurred around the end of January 1845, in a public hall on Washington Street, Boston.