Abstract.Because the syndrome of inappropriate antidiuretic hormone (SIADH) is a state of disturbed body fluid volume regulation and altered sodium balance we sought to determine if recently described volume regulatory factors were stimulated in SIADH. We measured atrial natriuretic peptide (ANP), endogenous digitalis‐like natriuretic factor (EDNF) and urinary free dopamine in SIADH (n= 27). We also determined fractional clearance of lithium (FCLi). The data obtained in SIADH were compared with similar measurements performed in sodium retaining hyponatremias, such as those of heart failure (n= 26), liver cirrhosis (n= 19) and volume contraction (n= 28). We observed:ANP was 19.5 ± 2.7 µM/ml in SIADH; it was significantly lower than ANP in cardiac failure, but no different from ANP in volume contraction. Urinary free dopamine was 2.2 ± 0.8 µM/24 h in SIADH; this was significantly higher than in volume contraction and liver cirrhosis. EDNF (259 ± 42 nM/24 h) and FCLi (21.4 ± 2%) were both numerically higher in SIADH than in other hyponatremic disorders; however, the differences did not achieve significance. In conclusion, our observations did not establish a specific role of ANP in chronic stable SIADH. As to the importance of EDNF, dopamine and proximal tubular fluid reabsorption (FCLi) additional work using acute volume changes may demonstrate their participation in the renal sodium handling of SIADH more clearly than our st