The bone response to two hydroxyapatite (HA) products (Osteogen and Alveograf) and a porous methacrylate resin material (HTR) in rats was compared. Fifty rats had four holes drilled in each iliac crest. The three alloplasts were placed in separate cavities and the fourth cavity was left empty as an absolute control. The survival times varied. The results were evaluated by subjective and histomorphometric analysis. Data were analyzed with ANOVA. There was a statistical difference in bone apposition between HTR and the HA products. The HTR was less osteoconductive, while HA consistently showed dense bone formation. The HA products are generally associated with greater bone formation, suggesting that HA is a better material for bone replacement than HTR. Schlagwörter: alloplasts, bone formation, hydroxyapatite, methacrylate resin