A Legionella-like organism (strain 798-PA-H, ATCC 35999) isolated from a lung aspirate was shown by DNA hybridization to belong to the species Legionella hackeliae. Growth, gas-liquid chromatographic, and physiologic characteristics were consistent with those of the type strain of L. hackeliae, Lansing 2 (ATCC 35250). However, 798-PA-H was minimally reactive with L. hackeliae direct immunofluorescence assay conjugate or slide agglutination test antiserum. Cross-absorption studies with 798-PA-H and Lansing 2 antisera supported placing 798-PA-H in a second serogroup of L. hackeliae.