SummaryThe clinical evolution of our cases, the X-ray findings and the agglutination titer of the Hirst reaction suggest the diagnosis of viral pneumonia due to Singapore influenza, although a secondary bacterial infection should not be excluded.One of our patients suffered a bacterial surinfection due to Staphylococcus aureus. This complication is extremely frequent and its importance has been stressed by Dutch workers (Mulder, Lankaster, Beeuwkes).