The Byzantine period of the history of medicine begins about the middle of the fourth century A. D. and retains some degree of importance up to or perhaps a little beyond the beginning of the eighth century. During this period of nearly four centuries there appeared on the scene five physicians whose writings form a very creditable part of the late Greek medical literature. The names of these authors are: Oribasius, Aëtius, Alexander of Tralles, Theodore Priscianus and Paulus Aegineta. _Oribasius._--The first physician named in this list, Oribasius, was born about the year 325 A. D. in Pergamum, an important city of Asia Minor and the birthplace of Galen. He received his medical training at Alexandria, settled in Constantinople (the new name given to Byzantium), and soon afterward became the personal physician of the Emperor Julian the Apostate, the nephew of Constantine the Great. Subsequently he was appointed Quaestor of Constantinople, but, upon the death of Julian (363 A. D.) and the accession of Valens and Valentinianus to power, his property was confiscated and he himself was obliged to take refuge among the Ostrogoths, who dwelt on the shores of the Black Sea. These people received him with open arms, and he soon acquired great influence among them. After a time, however, he was recalled to Constantinople and all his former privileges were once more granted to him. He died about the year 403 A. D. Despite his duties as a practicing physician of the very highest rank--duties which he could not wholly set aside when he accepted the office of Quaestor of Constantinople--and despite the necessity of devoting considerable time to the work which this non-medical official position entailed, Oribasius, like Pliny, appears to have been a most energetic contributor to medical literature. We possess to-day, for example, a large part of the medical cyclopaedia (72 books) which he prepared at the command of the Emperor Julian, and which--even in its incomplete state--contains very full information regarding anatomy, physiology, surgery, pathology and pharmacology. Although the work is simply a compilation, its present value is great, for it contains numerous extracts from earlier and contemporary treatises, many of which have entirely disappeared,--treatises of which we should have had no knowledge whatever if Oribasius had not introduced numerous extracts from them into his cyclopaedia.