Synthetic bone void fillers are gaining acceptance as graft extenders in spinal surgery. One such product is an ultraporous formulation of nanometer-sized particles of beta-tricalcium phosphate (beta-TCP). An ongoing prospective open-label, randomized, observer-blinded, comparative study evaluated the efficacy and safety of a novel beta-TCP bone void filler as an additive to autogenous bone graft material in patients undergoing spinal fusion. Posterolateral instrumented or noninstrumented spinal fusion was performed at a single level or multiple levels with or without additional interbody fusion. Patients received autogenous bone on 1 side and autogenous bone augmented with extender (in a 1:1 ratio based on the weight of the materials) on the opposite side, each patient serving as his or her own control. The graft material was placed at the level of the facet joints and the intertransverse processes. Patients were randomized to receive the extender on either the right or the left side. This article is a preliminary report on patients who have undergone this procedure.