Roles for urease in virulence are accepted for Helicobacter pylori and urinary tract pathogens. However, urease is widely expressed by bacterial and fungal lung pathogens causing emerging and opportunistic lung infections, organisms causing acute exacerbations of chronic bronchitis, mycobacterial lung diseases such as tuberculosis (TB), and ventilator associated pneumonia and health care associated pneumonia. Detection of urease provides a method for rapid in vivo detection of these lung pathogens by inhaled 13C- breath test, and this review discusses the range of lung pathogens that might be amenable to rapid diagnosis.