Objective: Algipore is a clinically established bone substitute. The present study evaluated the osseoconductive and resorptive characteristics of Algipore modified with collagen type I (ACI). Study Design: Three defects of 10 × 3 mm were set in the frontal bone of 10 adult female minipigs. One cavity was filled with commercially available Algipore, and the second with ACI. The third cavity was left unfilled and served as reference. After 4 months of healing, the animals were humanely killed. Bone formation and resorption characteristics of the substitutes were evaluated histomorphologically and histomorphometrically using Donath's sawing and grinding technique. Results: Neither material caused inflammatory reactions. Compared with controls, both substitutes showed significantly higher fractions of trabecular bone (control: 42.2%; Algipore: 58.7%, [P <.001]; ACI: 53.6%, [P =.013]). After 4 months, the remaining fraction of Algipore was 42.2% and the fraction of ACI was 47.9% (P =.016). Conclusions: The present study demonstrates that the modification of Algipore with collagen I does not show any benefits compared with pure Algipore in small calvarial bone defects in minipigs.