The clinical effects of topical negative pressure therapy (TNP) on wound healing are well described in numerous articles. While the mechanism(s) of action are not completely understood, it is postulated that reduction of local and interstitial tissue edema, increased perfusion of the (peri-) wound area, changed bacterial composition, and mechanical stimulation of the woundbed contribute to the clinical success. Our hypothesis is that with the removal of excessive fluid, proteolytic enzymes negatively influencing the healing process are removed. Our aim was to assess whether the concentrations of albumin, matrixmetalloproteinase-9 (MMP-9), and tissue inhibitor of metalloproteinase (TIMP-1) were different between wounds treated with TNP and conventional gauze therapy. We analyzed wound fluid samples of 33 wounds treated with either TNP therapy (n=15) or conventional therapy (n=18) on albumin, pro- and activated MMP-9, TIMP-1, and the ratio of total MMP-9/TIMP-1. Albumin levels were found to increase significantly in acute wounds compared with chronic wounds; however, no difference could be found on comparing TNP with conventional therapy. We did find significantly lower levels of pro-MMP-9 and lower total MMP-9/TIMP-1 ratio in TNP-treated wounds during the follow-up of 10 days. These data strongly suggest that TNP therapy influences the microenvironment of the wound.