Porcine small intestine evolved a specific offensive odor only 0.5 to 1 day after storage at 20 degrees C. We investigated the effects of Houttuyniae cordata (dokudami), refinery final molasses (RFM), green tea, and brown sugar on the evolution of methylmercaptan and ethanol, which were the main components of the volatiles which evolved from porcine small intestine in storage. Furthermore, we determined their antibacterial effect and deodorant activity against methylmercaptan, as possible factors in reducing the offensive odor. Addition of those materials reduced the offensive odor during storage. In particular, dokudami, green tea, and RFM markedly suppressed the evolution of methylmercaptan. RFM was most effective in suppressing the growth of bacteria. Dokudami had the highest deodorant activity, comparable to that of perilla leaves. However, the retardation of methylmercaptan evolution in situ cannot be simply explained by either of deodorant or antibacterial effect. It seems likely that the combined action of both effects affects the evolution of methylmercaptan in situ.