The invention relates to a process for the catalytic hydrotreating of a feed of oil origin, of diesel fuel type, in at least one fixed-bed hydrotreating reactor, for manufacturing diesel fuel, characterized in that incorporated into said feed are vegetable oils and/or animal fats up to a level of around 30% by weight, the mixture of said feed and vegetable oils and/or animal fats being introduced into the reactor operating in a single pass, without recycling liquid effluent at the top of the reactor.It also relates to a hydrotreating reactor for implementing said process, and to a corresponding hydrorefining unit.