Short-wave W-energy (100 p,W/cmZ) decreased the number of List&u monocytogenes on Tryptose Agar (TA) ca. seven orders of magnitude in 4 min. Age of culture (48 vs 24 hr) did not alter the sensitivity of Listeria to this W treatment. Increasing the intensity of irradiation (550 vs 100 pW/cm2) increased the rate at which L. monocytogenes was inactivated. Dry rather than moist cells of L. monocytogenes were most resistant to irradiation. In general, inactivation of Lisferiu with short-wave W-energy yielded sigmoidal survivor curves. The population of Listeria on TA plates was not affected with long-wave Wirradiation.