Abstract: Described are derivatives of the precursor peptide of the cardiodilatin/atrial sodiuretic factor (CDD-ANF) or fragments thereof which comprise at least the amino acid sequence of alpha-hANaP. The derivatives according to the present invention are compounds of the formula (I) ##STR1## X is a phosphate or thiophosphate group. R is NH.sub.2 or a peptide fragment from the amino acid sequence of gamma-hANaP. Radio-labelled derivatives are also possible. A method for the qualitative and/or quantitative determination of peptides containing the sequence of alpha-hANaP and a use of the compounds having the formula (I) as medicaments for various vaso- and renal related disorders are further described.