The goal in performing spinal fusion techniques is to achieve solid fusion, which will maximize clinical outcomes. This goal has generated enormous interest in developing bone graft alternatives or extenders that enhance or replace autologous bone graft. Autogenous bone graft from the iliac crest is still the gold standard for graft materials because it has all 3 properties essential for adequate fusion. The search for a synthetic graft as good as or better than iliac crest bone graft has recently intensified with the emphasis on minimizing the invasiveness of surgical techniques, including harvest of iliac crest autograft (such harvesting can be associated with significant donor site morbidity). Increasingly being studied are biologically active substances intended to extend, enhance, or even replace autologous graft. These substances include (a) allograft cancellous chips and (b) cortical spacers that are both osteoconductive (provide bone scaffold) and weakly osteoinductive (promote new bone formation), including demineralized bone matrix products. Human recombinant bone morphogenetic proteins (BMPs), including recombinant human BMP-2 (rhBMP-2) and recombinant human osteogenic protein 1 (rhOP-1 or rhBMP-7), are being investigated in human clinical trials and show promise as autologous bone graft substitutes. Synthetic bone grafts (ceramics), such as hydroxyapatite and beta-tricalcium phosphate, provide scaffolds similar to those of autologous bone, are plentiful and inexpensive, and are not associated with donor morbidity. Furthermore, adding silicon may increase the bioactivity of calcium phosphate and enhance interactions at the graft-host interface.