Abstract: The instant invention comprises an improved hydrorefining process which comprises contacting hydrocarbonaceous oil feed and hydrogen with a catalyst comprising a hydrogenation component selected from the group consisting of Group VIB metal component, Group VIII non-noble metal component and mixtures thereof, optionally comprising a phosphorous-containing component or compound, and an alumina-containing support, at hydrorefining conditions, wherein the improvement comprises heating the catalyst in substantially non-sulfided form at initial start-up from a temperature below about 450.degree. F. to hydrorefining temperature at an average rate of less than 30.degree. F. per hour in the presence of hydrogen and a start-up hydrocarbonaceous oil feed having a sulfur content in the form of organosulfides of greater than 0.5 moles (basis elemental sulfur) per kilogram of start-up feed.