The author portrayed the Officium of the Furnace, i. e. a liturgical depiction of the story of the Three Youths in a Fiery Furnace, once staged in the main churches of Constantinople and Thessaloniki as well as other metropolitan churches in Byzantium. He characterised the context of the performance, namely, the sung version of the Divine Service. He also cited information contained in manuscripts and described the arrangement of parts of the officium and its dramatic course. The author then wrote about the place held by the officium in question in the liturgical calendar, the means of its execution, the type of songs (alternate) and motion (dance) and probable props (furnace, icon). The article mentions the doubts harboured by members of the Church hierarchy about this particular form of the cult as well as the justifications of its defence. Finally, the author outlined the course of his own work on the reconstruction of this form, which had not survived in live tradition. The reader is offered additional information about the tradition of performing the Officium of the Furnace in Rus'.