Some newly emerging viral lung infections have the potential to cause large outbreaks of severe respiratory disease amongst humans. In this contribution we discuss infections by influenza A (H5N1), SARS and Hanta virus. The H5N1 subtype of avian influenza (bird flu) has crossed the species barrier and causes severe illness in humans. So far, 328 humans in twelve countries have contracted the disease and 200 have died. The young are particularly affected. Oseltamivir is the antiviral drug of choice and should be given as early as possible. Patients require supportive care, often including invasive ventilation. If H5N1 develops the ability to transmit efficiently between humans, an influenza pandemic is likely. Severe acute respiratory syndrome (SARS) was first seen in China in 2002. The outbreak was finally contained in 2003, by which time 8098 probable SARS cases had been identified with at least 774 deaths. The virus was identified in 2003 as belonging to the coronaviridae family. SARS is transmitted between humans and clusters have been seen. The mainstay of treatment is supportive. Various antiviral agents and adjunctive therapies were tried but none were conclusively effective. Hanta virus is an emerging cause of viral lung disease. In 1993, a new species of Hanta virus was recognized, after an outbreak of a new rapidly progressive pulmonary syndrome in the US, 465 cases of ‘Sin Nombre’ virus have now been seen in the US with a mortality rate of 35%. Many of the confirmed cases had contact with rodents (the major host of hanta viruses). Treatment is supportive, as there is no specific therapy.