OBJECTIVE: To compare the host response, architectural integration and tensile strength of polypropylene and porcine small intestine submucosa-derived implants in a rat model. DESIGN: Experimental study. SETTING: Center for Surgical Technologies, Faculty of Medicine, Katholieke Universiteit Leuven, Belgium. SAMPLE: Forty-eight adult male Wistar rats weighing 220-250 g randomised to receive either implant. METHODS: Full thickness abdominal wall defects were primarily repaired with polypropylene mesh (Marlex) (MX group) or porcine small intestine submucosa (Surgisis) (SIS group). Animals were sacrificed at 7, 14, 30 and 90 days after implantation. MAIN OUTCOME MEASURES: The presence of herniation, infection and intra-peritoneal adhesions. Change in thickness and tensile strength of implant. Histopathological and immunohistochemical appearances of inflammatory response and collagen deposition. RESULTS: Implants from the SIS group showed a short term increase in thickness in the first 14 days. Formation of adhesions was significantly more intense in the MX group at 30 days, and more extensive in the SIS group at 90 days. Tensile strength increased over time in both groups but was significantly lower in the SIS group than the MX group at 30 days. Implants in the MX group showed a more pronounced inflammatory response and more pronounced new vessel formation than the SIS group. Collagen formation was initially more fibrous and better organised in the MX group but became greater in the SIS group at 90 days. CONCLUSIONS: Biologically derived implant material induced a less pronounced inflammatory response and differences in collagen deposition. At 30 days tensile strength was weaker in the biological implant group but was equivalent by 90 days. These differences may have implications for the in vivo performance of the materials.