Ether anesthesia was introduced in Spain on January 13, 1847. Dr. Diego de Argumosa y Obregón, from Madrid, was the first Spanish surgeon who operated with the help of sulphuric ether. Almost at the same time, by the end of January, the dentist Oliverio Machechan administered ether to 2 patients in whom he performed dental operations. Subsequently, ether was used in several parts of Spain: Barcelona, Pamplona, Motril, and by several Madrid surgeons through February and March. In Santiago de Compostela ether was also introduced very soon, and, on the basis of the data from the studies of Dr. José González Olivares (the surgeons who first tried it in that town), most authors dealing with this issue state that it was probably in Santiago de Compostela where these experiments were carried out simultaneously with those by Argumosa in Madrid or even before. We have in some occasions defended that thesis; however, we were not satisfied with it and we decided to reinvestigate the facts. We had access to other sources and we concluded that anesthetics were really used a very early phase in Santiago de Compostela, but in the case of ether it was later than Argumosa and Oliverio Machechan used it in Madrid and Mendoza in Barcelona. In the present article we analyze these facts in detail, with emphasis on those that we consider historically relevant and that had not been previously dealt with by any other author addressing these issues.