Summary:A study was made of the lungs of 13 patients who died of a respiratory illness commencing as clinical influenza during the severe epidemic of Hong Kong influenza in New South Wales in 1970.In nine patients A2/Hong Kong/68 virus was isolated from the lungs after death and in these, histological examination showed changes typical of influenza viral pneumonia. These changes appeared capable of reversal had the patients survived. In four further patients, whose clinical illness was generally of longer duration before death, there were similar histological changes in the lungs, together with more chronic changes that appeared unlikely to be completely reversible. Although virus was not cultured from their lungs and the only direct evidence for influenzal cause was a high titre of serum antibodies found in one patient during life, it was thought that viral infection was responsible for the chronic pulmonary damage in these patients.In view of these findings it is suggested that some patients who survived similar prolonged clinical illness in this or other epidemics may well have sustained irreversible damage to areas of lung. Influenzal pneumonia may therefore occasionally cause permanent pulmonary scarring and even perhaps contribute to the cause of “scar cancer