Over the past two decades there has been numerous new associations between chronic diseases traditionally considered non-infectious with infectious agents. This list of diseases include peptic ulcer, coronary heart disease, neuropsychiatric disorders, haematological disorders and malignancies. These associations have been made possible through improvements in diagnostic tests based on molecular biology techniques. The discovery of these associations is important as it opens up exciting opportunities for the prevention and treatment of many diseases hitherto considered incurable.