Tryptose broth containing 0.0, 0.05, 0.15, or 0.3% potassium sorbate was acidified to pH 5.0 or 5.6 with acetic, tartaric, lactic or citric acid; inoculated to contain ca. 103 CFU Listeria monocytogenes/ml; and incubated at 13 or 35°C. The pathogen was inactivated in tryptose broth containing (a) 0.3% sorbate and acidified to pH 5.0 with acetic, tartaric, lactic, or citric acid although the time required for inactivation varied from ca. 30 h to > 10 d and (b) 0.15% sorbate and acidified to pH 5.0 with tartaric acid. Growth of the pathogen was inhibited to various degrees by other combinations of sorbate and organic acids. L. monocytogenes grew at pH 5.6 regardless of organic acid or incubation temperature used and at pH 5.0 in all instances except when acetic acid and incubation at 13°C were used.