The objective of the research was to determine the optimum application rates of soybean peroxidase (SBP) plus peroxide (SBPP) for reducing odorous VOC emissions from swine manure. Industrial-grade SBP was applied in combination with liquid hydrogen peroxide (H2O2) or powdered calcium peroxide (CaO2) to standard phenolic solutions and swine manure, and emissions were measured in a wind tunnel. The primary odorant in the untreated manure was 4-methylphenol, which accounted for 68-81% of the odor activity value. At the optimum application rate of SBPP (50 g L-1), 4-methylphenol emissions were reduced from the swine manure by 62% (H2O2) and 98% (CaO2) after 24 h (P < 0.0001). The CaO2 had a longer residence time, remaining effective for 48 h with 92% reduction in emission rates (P < 0.0001), while H2O2 was similar to the control at 48 h (P = 0.28). (C) 2012 Elsevier Ltd. All rights reserved.