Three patients had diffuse reticulonodular shadowing on chest roentgenogram, dyspnea, cough, purulent sputum, airways obstruction, variable fever, and leukocytosis. Lung tissue from two showed inflammatory exudate in bronchioles and peribronchiolar alveoli; all had multiple isolates of eitherHaemophilus influenzaeorStreptococcus pneumoniaefrom sputum or lung tissue. When examined in the context of similar syndromes reported by others under different labels in the past, these observations suggest that this is a specific clinical entity, which is both uncommon and serious. Despite initial misdiagnosis in all three cases, the two patients in whom the true nature of the disease was promptly recognized had complete recovery after the institution of appropriate antibacterial therapy. The most accurate and appropriate term for this entity is diffuse bacterial bronchiolitis with bronchiolar pneumonia.