Method for filling syringes having a plunger made of an elastically deformable material provided with a seat for a removable control shaft controlling sliding of said plunger within the barrel of the syringe, said barrel comprising an opening for entrance of plunger provided with an edge, said method comprising the steps of: - providing an instrument removably coupled to the syringe and equipped with: - coupling means for removably coupling said instrument to said seat of the plunger, said coupling means being firmly attached to one of the ends of an externally threaded shaft, - an actuating grip nut provided with an internally threaded through-hole through which said threaded shaft passes and comes into engagement, said internally threaded through-hole provided in the actuating grip nut comprising a thread having the same pitch as the thread of the threaded shaft; - an optional supporting annular ferrule having a through-hole for the sliding of the threaded shaft, said supporting annular ferrule comprising an engagement surface for the barrel of the syringe; - engaging said coupling means with said seat of the elastically deformable plunger; - causing said grip nut to come into abutment against edge of opening of the base of the syringe barrel at the opening for entrance of the plunger into the barrel or, if present, against said optional ferrule located between the grip nut and the syringe barrel; - rotating said grip nut, when the coupling means are engaged within the seat of the plunger and the actuating grip nut is in contact with the barrel of the syringe or with said ferrule, thus causing threaded shaft to axially slide inside hole of grip nut and withdrawal of the plunger in the barrel of the syringe, this resulting in suction of liquid through the syringe tip. - providing an instrument removably coupled to the syringe and equipped with: - coupling means for removably coupling said instrument to said seat of the plunger, said coupling means being firmly attached to one of the ends of an externally threaded shaft, - an actuating grip nut provided with an internally threaded through-hole through which said threaded shaft passes and comes into engagement, said internally threaded through-hole provided in the actuating grip nut comprising a thread having the same pitch as the thread of the threaded shaft; - an optional supporting annular ferrule having a through-hole for the sliding of the threaded shaft, said supporting annular ferrule comprising an engagement surface for the barrel of the syringe; - coupling means for removably coupling said instrument to said seat of the plunger, said coupling means being firmly attached to one of the ends of an externally threaded shaft, - an actuating grip nut provided with an internally threaded through-hole through which said threaded shaft passes and comes into engagement, said internally threaded through-hole provided in the actuating grip nut comprising a thread having the same pitch as the thread of the threaded shaft; - an optional supporting annular ferrule having a through-hole for the sliding of the threaded shaft, said supporting annular ferrule comprising an engagement surface for the barrel of the syringe; - engaging said coupling means with said seat of the elastically deformable plunger; - causing said grip nut to come into abutment against edge of opening of the base of the syringe barrel at the opening for entrance of the plunger into the barrel or, if present, against said optional ferrule located between the grip nut and the syringe barrel; - rotating said grip nut, when the coupling means are engaged within the seat of the plunger and the actuating grip nut is in contact with the barrel of the syringe or with said ferrule, thus causing threaded shaft to axially slide inside hole of grip nut and withdrawal of the plunger in the barrel of the syringe, this resulting in suction of liquid through the syringe tip.