With the recent availability of an immuno-assay that measures the more stable ADH precursor peptide CT-ProVasopressin showing a close correlation with ADH blood levels [17,18], we sought to investigate whether elevated ADH precursor levels would causatively explain the typical low blood sodium levels of patients with Legionnaires’ disease in a large and well defined cohort of CAP patients from a previous trial [19]. This evidence concerns the gene AVP and Legionnaires' disease.