Vacuum gasoils are heavy petroleum cuts that are hydrotreated prior to being transformed into valuable fuels by hydrocracking. Hydrotreatment is a refining process carried out to reduce the content of heteroatomic molecules in petroleum cuts to meet the stringent fuel specifications and to prevent catalyst poisoning in downstream conversion processes. Kinetic modeling of hydrotreatment reactions requires information about the distribution of nitrogen compounds in vacuum gasoils and in their hydrotreated effluents. Analysis of heavy distillates is a challenge since nitrogen molecules are present in small amounts in the hydrocarbon matrix. Moreover, a large number of isomers are distributed over a large boiling point range (350-650 degrees C). This paper presents a GC-NCD method developed to determine the nitrogen distribution in vacuum gasoils. To validate the GC-NCD results, vacuum gasoils, narrow cuts as well as hydrotreated vacuum gasoils, have been analyzed. Quantitative data were compared to the total nitrogen content determined by organic elementary analysis, and an excellent agreement between both methods was found.