Presented in the work are four mediaeval privileges about the use of authentic seals which the Hungarian-Croatian kings, Louis I (1342-1382) his daughter, Queen Mary (1382-1385, 1386-1395) and her husband, Sigismund of Luxemburg (1387-1437) distributed to the Zagreb, Trogir and Senj chapter, in order that they could freely and in a legal basis carry out the service of public activities as Croatian loca credibilia (locations of authentication) which until then they carried out on the basis of the legalised decree of King Andrew II from 1231. This law applied to all our and Hungarian chapters and individual monasteries in the region of the mediaeval Hungarian-Croatian kingdom. The privilege of the Senj chapter, which performed public activity up until the18th century was certified in 1480 by Matthias I Corvinus (1458-1490) and after him in 1647 byEmperor and King Ferdinand III (1625-1657).