Wild-type Legionella pneumophila grows in human macrophages within a replicative phagosome, avoiding lysosomal fusion, while nonreplicative mutants are killed in lysosomes. Wortmannin, a phosphatidylinositol 3-kinase (PI3K) inhibitor, blocks phagocytosis of an avirulent mutant, but not of wild-type L. pneumophila, without affecting membrane ruffling and actin polymerization. These results show that wild-type and mutant Legionella strains use different entry pathways. They suggest that PI3Ks are involved in phagocytosis of an avirulent L. pneumophila mutant and regulate the ability of microorganisms to generate a replicative phagosome.