Introduction. Standard negative pressure wound therapy (NPWT) has been shown to help close wounds despite increasing planktonic bioburden. Both planktonic and biofilm critical colonization are associated with delayed wound healing; therefore, reducing microbial colonization is thought to aid wound healing. The use of NPWT with topical antimicrobial irrigation solution has previously shown reduction in quantitative planktonic bioburden when combined with sharp debridement in chronic wounds. Objective. The goal of this study was to evaluate the effectiveness of NPWT with instillation (NPWTi) on biofilm of chronic wounds. Materials and Methods. A prospective, randomized trial was conducted. Following sharp debridement, 20 patients with chronic wounds were randomized to 1 week of either NPWTi with 0.125% sodium hypochlorite solution (n = 10) or NPWT without instillation (n = 10). Serial wound biopsy was performed predebridement, postdebridement, and after 1 week of study therapy to test for quantitative nonplanktonic or biofilm-protected bacteria. Results. As expected, there was no difference in change in wound size between the 2 groups at 1 week. The NPWTi group had a mean reduction in quantitative biofilm-protected bacteria of 48%, while the NPWT without instillation group had a mean increase of 14% (P < .05). Discussion. Consistent with previous studies, this trial demonstrates that NPWTi with dilute sodium hypochlorite solution is effective at reducing nonplanktonic bioburden of chronically, critically colonized wounds. Conclusion. Therefore, based on this and previously published work, this therapy provides both planktonic and nonplanktonic bioburden reduction as well as NPWT benefits and may be a tool for the preparation of infected wound beds prior to definitive closure.