Abstract The ‘Four Levels’ term refers to the four levels of depth in the development of fevers from acute infectious diseases. It is a brilliant theory of Chinese medicine that was developed during the early Qing dynasty by Ye Tian Shi in his book ‘A Study of Warm Diseases’ (Wen Bing Xue, 1746). In my opinion, the theory of the Four Levels provides the key to an understanding of acute, febrile, infectious diseases. This article will highlight the application of the theory of the Four Levels to the diagnosis and treatment of H1N1 influenza (‘swine flu’). Key words: Swine Flu, H1N1, Influenza, Wen Bing, Four Levels