Abstract: The invention relates to a process for hydroconversion in a reaction zone (preferably in a bubbling bed and/or in slurry) of liquid heavy hydrocarbon feedstocks containing sulphur, in the presence of hydrogen and a catalytic solid phase, said solid phase being obtained from a catalytic precursor, a process in which the catalytic precursor is injected into a part of the liquid conversion products which contain dissolved hydrogen sulphide, asphaltenes and/or resins, under temperature and pressure conditions close to those at which they leave the reaction zone, and the obtained mixture is injected into the reaction zone. Preferably, the catalytic precursor is injected into the part of the conversion effluents that is recycled to the reactor inlet. The invention also relates to a device that can be used for implementing this process.