The bluntedresponse to antidiuretic hormone (ADH) in nephrogenic diabetes insipidus secondaryto lithium-treatment reduces the effect of SIADH, and high dose lithium-therapy hashistorically been used to treat hyponatraemia secondary to this condition (White and Fetner, 1975).Whether lithium therapy in a psychiatric context reduces the risk of severehyponatraemia is still unknown. Here, AVP is linked to inappropriate ADH syndrome.