A method for manufacturing a monolithic hollow body by means of a casting or injection moulding process, the manufacturing method comprising the steps of: producing at least one lost ceramic core that reproduces the shape of at least one internal cavity of the hollow body by forming the "green" ceramic core; establishing a firing temperature for the "green" ceramic core that allows the ceramic core to gain a mechanical strength that is higher than the mechanical stresses on the ceramic core in use; heating the "green" ceramic core to a temperature that is equal to the previously established firing temperature to fire the ceramic core and give the ceramic core its final mechanical characteristics for utilization; introducing the ceramic core inside a first mould which reproduces in negative the external shape of the hollow body; feeding a molten material inside the first mould by means of a casting or injection moulding process; letting the material inside the first mould solidify; extracting the hollow body from the first mould; and destroying and removing the ceramic core located inside the hollow body; the manufacturing method being characterised in that the production of the ceramic core comprises the further steps of: determining how the bending mechanical strength measured in MPa of the ceramic core changes as the firing temperature varies; estimating in advance the mechanical stresses on the ceramic core when the ceramic core is handled and when the molten material is fed inside the first mould; and establishing, once the mechanical stresses on the ceramic core when the core is handled and when molten material is fed inside the mould have been estimated, the firing temperature for the "green" ceramic core that allows the ceramic core to gain a minimum possible mechanical strength that is higher than said maximum mechanical stresses on the ceramic core when the ceramic core is handled and when the molten material is fed inside the first mould so that the ceramic core correctly resists in the casting or injection moulding process and, at the same time, has the minimum possible resistance to subsequent destruction and removal from inside the hollow body. producing at least one lost ceramic core that reproduces the shape of at least one internal cavity of the hollow body by forming the "green" ceramic core; establishing a firing temperature for the "green" ceramic core that allows the ceramic core to gain a mechanical strength that is higher than the mechanical stresses on the ceramic core in use; heating the "green" ceramic core to a temperature that is equal to the previously established firing temperature to fire the ceramic core and give the ceramic core its final mechanical characteristics for utilization; introducing the ceramic core inside a first mould which reproduces in negative the external shape of the hollow body; feeding a molten material inside the first mould by means of a casting or injection moulding process; letting the material inside the first mould solidify; extracting the hollow body from the first mould; and destroying and removing the ceramic core located inside the hollow body; the manufacturing method being characterised in that the production of the ceramic core comprises the further steps of: determining how the bending mechanical strength measured in MPa of the ceramic core changes as the firing temperature varies; estimating in advance the mechanical stresses on the ceramic core when the ceramic core is handled and when the molten material is fed inside the first mould; and establishing, once the mechanical stresses on the ceramic core when the core is handled and when molten material is fed inside the mould have been estimated, the firing temperature for the "green" ceramic core that allows the ceramic core to gain a minimum possible mechanical strength that is higher than said maximum mechanical stresses on the ceramic core when the ceramic core is handled and when the molten material is fed inside the first mould so that the ceramic core correctly resists in the casting or injection moulding process and, at the same time, has the minimum possible resistance to subsequent destruction and removal from inside the hollow body. determining how the bending mechanical strength measured in MPa of the ceramic core changes as the firing temperature varies; estimating in advance the mechanical stresses on the ceramic core when the ceramic core is handled and when the molten material is fed inside the first mould; and establishing, once the mechanical stresses on the ceramic core when the core is handled and when molten material is fed inside the mould have been estimated, the firing temperature for the "green" ceramic core that allows the ceramic core to gain a minimum possible mechanical strength that is higher than said maximum mechanical stresses on the ceramic core when the ceramic core is handled and when the molten material is fed inside the first mould so that the ceramic core correctly resists in the casting or injection moulding process and, at the same time, has the minimum possible resistance to subsequent destruction and removal from inside the hollow body.