EN
The article examines three handwritten partbooks, formerly property of the Braniewo Jesuit Collegium, taken in 1626 as a war trophy with other manuscripts and prints by the invading Swedes to Stockholm and held in the University Library of Uppsala. In comparison to the majority of polyphonic arrangements of 'proprium missae', typical of the European tradition, which are characterized by clear and logical system corresponding to the liturgical year, the manuscript 'UppsU 76f' seems chaotic, with several irregularities. The analysis of its features leads the authoress to the hypothesis that it could have been created in a Protestant-influenced region. Some similarities are found with 'Choralis Constantinus' by Heinrich Isaac and with the oldest polyphonic manuscript of the Wawel chapel, dated by Mirosław Perz and Elzbieta Zwolinska as of mid-16th century. Although none of the compositions in the Braniewo manuscript bears its composer's name, in some instances concordances were found. The authoress identifies further works and provides other information on the collection, such as dating, hypotheses concerning its origin and the reasons of its importance for Polish and European culture.