There is an increasing body of work in the literature which documents the relationship between Legionella and protozoa. Recent research points to the possibility that the protozoa can serve as hosts to Legionella, thereby providing an environment in which Legionella can multiply while being protected from biocides. While several studies examined the efficacy of commonly used biocides against protozoa the efficacy of glutaraldehyde had not been determined. This paper will detail the efficacy of
glutaraldehyde and a glutaraldehyde/quatemary amine blend along with several different commonly used water treatment biocides against both pure protozoam strains and field isolates. Keywords: amoebae, biocides, glutamldehyde, Legionella, protozoa