In the article an attempt is made to revise the opinion that the apocrypha are the local, popular, even layman literature of the Middle Ages. Their place in the Old-Bulgarian literature is defined. They acquire the status of “rejected” books together with the final formation of the canonic biblical corpora, accompanying the institutionalization of the Christianity. The genre peculiarities of the apocryphal texts remain parallel to the biblical. The new information in the apocrypha on biblical persons and events is classified, and the following main groups are determined: information, complementing the biblical story with details aiming to explain the respective episodes of the canonic texts; a doubling story about events described in the canonic texts, including new motives or different variants of biblical motives; a detailed story about events marked in the canonic texts; free interpretation of biblical motives, as the biblical variant refers to completely different people and events; interpretation of motives and images from the pre-biblical mythology of the Jews or from mythologies of neighbouring peoples. The Byzantine text of Apocalypses of Moses and the Old-Bulgarian text of Oration for Adam and Eve are compared. An opinion is expressed that in this case there is rather a free retelling with new added elements. Special attention is paid to the Secret Book of the Bogomils, offering a peculiar code for realizing the information from the canonic and some apocryphal texts. This bears record of the high erudition of its author, as well as of the narrow circle of readers, it was intended for. A testimony for the author’s self-esteem is also the approach to the source material of presbyter Jeremiah, who giving a new meaning to the motive of the grateful dead man, builds a new plot on the text of the biblical book Tovit. Special attention is paid to the texts which include motives and plots taken from the oral narratives of the Middle Ages, and there is an opinion that in this case we cannot talk about insufficient theologian erudition of the relevant authors, but about literary fashion. As a result of the studies done, it is concluded that the apocryphal literature has been translated and read exclusively by highly educated scholars, searching “a different point of view” towards the biblical events, or offering a new interpretation of well-known biblical events. Regarding the influences between folklore and apocrypha within the framework of the Bulgarian medieval culture, they have been realized solely towards folklore – literature. This is the only way to explain the presence of motives, missing in the Judean-Christian tradition (canonic, non-canonic and anti canonic) in the Bulgarian apocrypha. At the same time the Christianization of the Bulgarian traditional culture was done mainly under the impact of the official church sermon.