We included 8 healthy volunteers with a total of 30 plasma copeptin measurements (8 at baseline and 22 with rising plasma osmolality until serum sodium > 147 pmol/l), 40 patients with polyuria-polydipsia syndrome, 20 patients with primary polydipsia and 20 patients with complete central diabetes insipidus, with a total of 80 copeptin measurements (40 basal and 40 osmotically stimulated copeptin measurements), and 40 severely ill patients with community acquired pneumonia, with a total of 40 copeptin measurements (all on admission to the medical emergency department). This evidence concerns the gene AVP and Central diabetes insipidus.