A little-known thirteenth-century manuscript preserved in Damascus contains by far the largest Syriac medical work that has survived till today. Despite the missing beginning, a preliminary study of the text allows us to argue that it is the medical handbook (entitled Kunnāšā) of Īšō' bar 'Alī, a ninth-century physician and student of Ḥunayn b. Isḥāq. The seven books of the handbook appear to follow the model of Paul of Aegina's Pragmateia both in composition and content. The actual significance of the handbook in the history of Syriac and Arabic medicine is yet to be assessed, but there can be no doubt that it will be a pivotal source that illustrates the development of Syriac medicine during a period of four centuries at the moment when it was being translated to lay the foundations of the nascent medical tradition in Arabic.