Date are presented, as a preliminary report of a study of the ocurrence of Listeria monocytogenes, in twenty samples of sewage water collected from affluents of two different sewage treatment station. A scheme for the isolation of the bacterium involving different selective media and employing Gray's cold incubation technique has been used for the purpose. In two opportunities, Listeria were isolated and the serological study of these strains were indentified as serotypes L4b and L4ab.