René Charbonneau (1643-72) traveled to Siam (modern-day Thailand) in 1676 as a lay auxiliary to a band of French missionary priests. It was intended that he would practice his skills as a surgeon to treat missionaries and the indigent poor in the mission hospital established in Ayutthaya. An examination of the few letters that survive in his hand reveal fascinating insights into some of the treatments he used.Details emerge which suggest how far healers like Charbonneau were transformed as they moved into new contexts: how they were able to experiment with new techniques and cures, and how they were often required to reconceptualize their approaches for new audiences. This article explores Charbonneau's life and career in seventeenth-century Ayutthaya to reassess the "foreign" healers in the history of Thai medicine, and to explore the methodological complexities of reconstructing the medical world of Ayutthaya.In 1730 an ecumenical funeral was held in Ayutthaya, the royal capital of Siam (modern-day Thailand). Present were representatives of various Catholic communities -Portuguese, French, Vietnamese, Spanish, and Siamesethe Protestant head (Opperhoofd) of the Dutch factory and his assistant, and various "people of other religions". 1 The man being laid to rest was René Charbonneau (c. 1646-1730), a "venerable elderly gentleman" of eighty-four, whose passing was "regretted by all the Christians and even the pagans". 2 Charbonneau was born in Les Herbiers, Poitou, France, the son of a tenant farmer. 3 By the time of his death he had lived in Siam for over fifty years. Fluent in Thai and knowledgeable about the country, his advice was sought by locals and by visitors. 4 He was probably known to the Siamese by the noble title ok phraya (ออกพระยา), and addressed as chaokuhn (เจ้ าคุ ณ, "lord"): honors granted by the former king, Phra