Paracelsus (d. 1541) was one of the first physicians to pose a lasting challenge to the foundations of medicine as it had been practiced for two millennia in Europe, North Africa, and West and South Asia. Rejecting authority, Paracelsus replaced Hippocrates’ and Galen’s elements and properties by alchemical principles and astrological correlations, refusing to use Latin and instead publishing in German – although some followers wrote about his theories again in Latin, making them available to an international audience. A century after Paracelsus, Salih b. Nasrallah (d. 1670), who claimed knowledge of Latin, made numerous references to the “new,” or “chemical,” medicine, including inorganic drugs to his pharmacopeia. While his writings survived in numerous copies, much less is known about the actual application of his innovations in medical treatment, beyond the fact that raw material for alchemical drugs were being traded during (and already before) his period of activity. In the early 18th century, “chemical” medicine was prominent enough in the Ottoman Empire to come to the attention of the Sultan, who banned its use for a number of years. However, in the second quarter of the century, its fortunes returned, and it was in this period that we see the activities of Bursalı Ömer Şifai (d. 1742), whose oeuvre is at the center of the research project presented in this talk. Ömer Şifai left a large number of writings, mostly in Turkish, though some important texts also survive in Arabic. The best known work is a short treatise with drug recipes and advice for their use, based on Paracelsian principles. The existing bibliography of his writings is sketchy. Thus, the project presented here undertakes a review of available manuscripts, mainly from Turkey, based on autopsy, and investigates the relation to Ömer Şifai’s sources, both traditional (e.g., his massive pharmacopeia based on Ibn al-Baytar) and innovative (e.g., Paracelsus and his followers). In his period, Galenic and Avicennan approaches were clearly dominant in the Islamic world, and to a great extent in Europe as well. The reaction to challenges like that of Paracelsianism often were subtle, incorporating individual drugs rather than opening the conceptual foundations to discussion. The activities of Ömer Şifai as a doctor, writer, and translator shed light on a crucial period for the development of medical practice in the Ottoman Empire at a time when in Europe, too, the break with humoral medicine and the Galenic tradition is developing.