The influence of Nisaplin, which contains 2.5% nisin, on the growth of Listeria monocytogenes in Karashi-mentaiko (red-pepper seasoned cod roe) was investigated. The MICs of Nisaplin for L. monocytogenes (10(8) CFU/mL) were measured; seven isolates showed a value of 1,600 mu g/mL and one isolate showed a value of 800 mu g/mL. All L. monocytogenes isolates had a MIC of 800 mu g/mL at 10(6) CFU/mL. The number of L. monocytogenes in Karashi-mentaiko stored at 4 degrees C was decreased by Nisaplin added at 60 and 600 mu g/g. These results indicated that Nisaplin effectively inhibits the growth of L. monocytogenes in Karashi-mentaiko.