In this article the principal reason for the emigration of Dr. Carl Koller is examined on the basis of the available literature. In fact, antisemitism did not play a crucial role. After his colleague, Dr. Fritz Zinner, called him an impudent Jew in public in the General University Hospital of Vienna, Koller reacted by hitting the man in the face. A duel with heavy sabres was the outcome; Koller was unharmed, whilst his opponent received two deep gashes. Such duels were strictly forbidden at that time already, but were nonetheless still executed. In consequence, Koller's hopes of obtaining a position in the Eye Department, for which he was very well qualified, and of an academic career in Vienna were dashed and he had to emigrate. Koller eventually settled in New York in 1888, where he received many distinctions during his life span. The Medical Association of Vienna also honoured him in 1930. Dr. Koller was proposed several times for the Nobel prize in Physiology and Medicine, since his discovery of cocaine as local anaesthetic in ophthalmology was undoubtedly worthy of this prize, but his discovery had been published too long previously, so that according to the statutes of the Nobel prize this distinction could not be granted. Hence, it can be concluded that although Dr. Koller was forced to leave Vienna in 1885, it was not principally for antisemitic reasons. There were Jewish professors in the Medical Faculty of Vienna University at the time and, indeed, when the author studied medicine in 1931 to 1936, four Jewish professors held chairs in Vienna and one of his predecessors as chief of the First Department of Ophthalmology, Isidor Schnabel, was Jewish.