Melanoidin, which was obtained by the Maillard reaction between D-glucose and glycine, was found to exert a potent inhibitory effect on the activity of trypsin with BANA as a synthetic substrate. The concentration of melanoidin required to reduce the activity of trypsin by 50% was less than 1 μg/ml, similar to that of soybean trypsin inhibitor and leupeptin. On the other hand, chymotrypsin was not affected by melanoidin. The specific interaction between melanoidin and trypsin is discussed.