The bone marrow mixing instrument having a handle housing with a trigger mounted thereto. The handle housing contains a ratchet drive feed mechanism with a pawl assembly and a moveable ratchet bar. The other end of the ratchet bar is secured to a mixing housing which holds syringes filled with material and defines channels leading from the syringe area to a mixing nozzle removably mounted to the mixing housing. A piston rod and piston are mounted in each syringe containing bone defect material with a piston being advanced within the respective syringe by the feed mechanism to discharge bone defect material from the syringe into the adjacent channels in the mixing housing and into the mixing nozzle.