The Byzantine romance Barlaam and Ioasaph relating the conversion to Christianity of an Indian Prince, modelled on the life of Buddha, was very popular in the Middle Ages and later, for several centuries, but today is known to few people. Discussion of authorship and time of its composition, started by Hermann Zotenberg in the 1880s, has continued until today, without satisfactory conclusions. He cast doubt on the commonly held hypothesis that the work was written by St. John of Damascus. One of the main arguments adduced by the supporters of this thesis was presence in the romance of multiple passages from works by Gregory of Nazianzus, who St. John used to quote often. In this article I analyse the fragments of his Orationes which can be recognised in the text of Chapter XXIV, seeking answer to the question of how great was the dependence of its author (or editor) on this father of the Church and how his writings were used.