The composition of nitrogen bases of vacuum gas oil and hydrogenation products obtained at 360 and 380A degrees C is studied. The nitrogen bases of the initial distillate are represented by nitrogen and nitrosulfur compounds, the major part of which consists of benzoquinolines and thiophenoquinolines. The characteristic features of the nitrogen bases of the hydrogenation products are absence of nitrogen- and sulfur-bearing structures, increased content of poorly substituted quinolines, appearance of mononaphthenopyridines and mononaphthenoquinolines, and reduced benzoquinoline content. Elevation of vacuum gas oil hydrofining temperature from 360 to 380A degrees C causes increased yield of concentrate of extractable nitrogen bases. The qualitative composition of the extracted bases remains unchanged in this case, and the differences occur only in the relative content of various types of compounds.