A method for knocking out a foundry core confined in an internal cavity in a part at the end of a casting operation, comprising at least a primary chemical knocking-out step during which the part is subjected to a chemical solution to dissolve the core, in a sealed enclosure or autoclave, the method further comprising a secondary step of knocking out by ultrasounds during which the part is immersed and subjected to ultrasounds in water or an aqueous solution contained in an ultrasound tank to loosen core residues from walls of the cavity.