This article discusses previously undocumented examples of music for the old Beneventan divine office in a manuscript housed in the Archivio Storico Diocesano in Naples (Cod. Misc. 1, fasc. VII). The breviary, which was copied at the scriptorium of Santa Sofia, Benevento, in 1161, transmits two unica —canticle antiphons for the feast of St. Mercurius—in Beneventan style. It also preserves a Beneventan-style antiphon for the Holy Twelve Brothers of Benevento that is not transmitted in previously published sources of Beneventan chant. The discovery of music in Beneventan style for St. Mercurius is of importance to the history of the old Beneventan rite, as it attests to the continued production of the distinctive formulaic style of the Beneventan rite into the later eighth century. The relics of Mercurius, a military saint of Byzantium, were enshrined at the altar of Santa Sofia at Benevento in 768, and Mercurius was adopted as patron of the court, the church of Santa Sofia, and the city of Benevento. Despite the establishment of the cult of St. Mercurius in the second half of the eighth century, until now no musical record has indicated the presence of old Beneventan music for this feast (there is no extant Beneventan mass proper for Mercurius, and the documented sources for the divine office preserve only Romano-Beneventan or neo-Gregorian-style music). I consider the St. Mercurius antiphons within the context of the musical style of the old Beneventan rite and argue that they should be included in the Beneventan canon on the basis of musical style. As pitch-specific exemplars of the distinctive formulaic style of the Beneventan chant, this source is of particular value to the study of Beneventan pitch and modality. Notated in fully heightened Beneventan neumes on a staff line, these antiphons are among the few surviving witnesses of the old Beneventan repertory that preserve the distinctive modal properties of the repertory in pitch-specific notation. I introduce the music of these antiphons and consider their importance as witnesses to the continued production and copying of Beneventan music from the late eighth to the twelfth centuries.