Dysgonic fermenter 2 (DF-2) is a fastidious, gram-negative organism well recognized as a cause of fulminant septicemia in patients without spleens or patients with alcoholic cirrhosis. In vitro antibiotic susceptibility testing of eight strains with a Schaedler broth dilution technique revealed DF-2 to be susceptible to all of the antibiotics tested except aztreonam. Previous reports that DF-2 is aminoglycoside resistant were based on disk diffusion or agar dilution assays that may be less reliable given the slow growth of the organism and its requirement for CO2 incubation. Penicillin is commonly used as prophylaxis after dog bites and has excellent activity against DF-2.