The author had the detection of the exact version of the troparion to Achillius of Larissa as his initial idea, as he noticed that the modern singing of this hymn in the church in Arilje was not correct. Following this course he briefly presents the results obtained by previous researchers, including those of Tatjana Subotin Golubović. Recognizing the original text of the troparion in the service of the author Nikodim from the 14th or 15th century, he pointed out the perceived differences and published the contemporary Serbian translation on the basis of that version, aided by Zoran Ranković, a professor of the Theological Faculty in Belgrade. The study outlines the fact that the church in Arilje is missing a significant historical document known as The Rules of St. Achillius containing Saint’s service in Church Slavonic originating from 1850. The document was copied by Đorđe Jovanović in the Monastery Blagoveštenje, and could surely be found in Arilje before 2000. Finally, prompted by the realization that there is no fully adequate and complete service to Saint Achillius that could be used during the celebration of the saint to whom the church in Arilje is dedicated, the author recommends possible solutions which go towards the creation of a modern liturgical artifact.