Pulmonary and systemic defenses against hematogenous challenge with ³²P-labeled Staphylococcus aureus were measured 10 min, 8 hr, and 24 hr after intravenous injection of the bacteria in a mouse model of influenza virus pneumonia. Infection with influenza A virus did not alter bactericidal defenses in the liver and spleen, but pulmonary bactericidal activity measured 24 hr after infection was suppressed in virus-infected animals; 20% ± 3% of the initially injected, viable bacteria were recovered from lungs of pneumonitic mice after 24 hr as compared with 9% ± 1% from lungs of the un infected mice. These data demonstrate that pulmonary infection with influenza virus does not alter antibacterial defenses of the liver and spleen but does suppress bactericidal activity in the lung.