ENIn this article, I discuss Joachim Lelewels achievements concerning his conception of the theoretical foundations of historical science. However, I have chosen to limit the subject to his earliest methodological inquiries, covering the period from his studies at the Imperial University of Vilnius (1804-1808) to the year in which he took up the post of deputy professor at the same university (1815). I have divided the article into two parts. In the first part, I briefly discuss J. Lelewels methodological interests during his studies and early scholarly activity (until 1815). In the second part, I compare an edition of Historyka rękopiśmienna with a microfilm of its manuscript to show that when analysing the Vilnius professors theoretical concepts of history, source editions should support the research, but cannot replace the manuscript. Keywords: Joachim Lelewel, methodology of history, critical edition of historical texts.