Abstract: A method of subjecting a middle-distillate hydrocarbon feedstock to a hydrotreating reactions to remove heteroatoms and/or hydrogenate aromatics, and apparatus therefor. The method comprising heating a liquid middle distillates hydrocarbon feedstock to produce a heated feedstock, mixing the heated feedstock with a hydrogen-containing treating gas to produce a mixture, and bringing the mixture into contact with a hydrotreating catalyst at an elevated temperature and an elevated pressure effective for hydrotreating the feedstock. The hydrogen-containing gas is mixed with the heated feedstock in a ratio effective to fully vaporize the liquid feedstock at the elevated temperature and pressure before the feedstock is contacted with said hydrotreating catalyst. Ideally, the mixture is passed through a catalyst bed creating a pressure drop in the gas mixture equal to or less than 0.3 bar/m. Such a catalyst bed may be made of structured catalysts, such as monolithic catalysts.