Legionella pneumophila, the Gramnegative bacterium that causes Legionnaires' disease, can be cultured in the laboratory in a variety of fresh-water amoebae and macrophage-like cell lines. None of these hosts, however, is amenable to genetic analysis, which has limited the ability of researchers to analyse the host factors essential for L. pneumophila growth, in this article, we describe a novel method in which L. pneumophila is grown within the soil amoeba Dictyostelium discoideum and how D. discoideum genetics is being used to analyse the host cell factors involved in L. pneumophila pathogenesis.