BACKGROUND Excisional wound healing in inducible nitric oxide synthase knockout (iNOS-KO) mice has been previously shown to be impaired compared with their background strain controls. Incisional wounds were created in this experiment in both types of animals and paradoxically were found to heal with the same rapidity and breaking strength in both groups. METHODS Dorsal 2.5 cm incisional wounds were created in iNOS-KO mice, as well as their parental strain controls (C57BL/6J). Standardized polyvinyl alcohol sponges were implanted in the wounds to allow for measurement of collagen deposition. Animals were harvested on postoperative days (PODs) 3, 5, 7, 10, 14, and 28, and their wounds subjected to tensiometric breaking strength analysis. Nonisotopic in situ hybridization quantitative analysis for iNOS, endothelial NOS (eNOS), basic fibroblast growth factor (bFGF), transforming growth factor-beta1 (TGF-beta1), vascular endothelial growth factor (VEGF), and interleukin-4 (IL-4) expression in the wounds was performed. Hydroxyproline levels were quantitated in the harvested polyvinyl alcohol sponges. Data were analyzed with the Students t test. RESULTS No significant differences were found in breaking strengths or levels of hydroxyproline (and thus collagen) in iNOS-KO versus wild-type wounds at all tested time points. Flawed iNOS expression levels in iNOS-KO animals were similar to (functional) iNOS expression in wild-types. eNOS and bFGF expression nearly doubled on POD 7 in iNOS-KO incisions (P =.002, and.002), respectively and remained 200% to 300% elevated thereafter. TGF-beta1 expression was increased approximately 50% to 100% in iNOS-KO wounds on PODs 5 and 7 (P =.006 and.01, respectively). VEGF and IL-4 expression was elevated by 25% to 100% in wild-type compared with iNOS-KO animals at all time points (P <.01). CONCLUSIONS The overexpression of TGF-beta1 and eNOS may represent mechanisms in iNOS-KO mice to compensate for their loss of functional iNOS, resulting in incisional wound healing equivalent to controls. Their impaired expression of VEGF and IL-4, on the other hand, may partially explain the delayed excisional wound healing noted in these animals.