The synthesis of three reactive analogues of [1,6-alpha-aminosuberic acid, 8-arginine]-vasopressin ([Asu1,6,Arg8]vasopressin) is described. Two peptide hormone analogues contain in the p-position of Phe2 the azido or 3-(3-methyl-3-diazirinyl)propanoylamino residue, which can be converted by photoactivation into nitrenes and carbenes, respectively. The third derivative contains the chemically reactive (bromoacetyl)amino group in the same position. The analogues are prepared via the precursor [Asu1,6,Phe(pNH2)2,Arg8]vasopressin, which is obtained by peptide synthesis in solution. Modifications of the p-amino group of Phe(pNH2) give the reactive analogues. The analogue containing p-azidophenylalanine in Pos. 2 shows a similar high binding affinity for the antidiuretic receptor in bovine kidney as vasopressin. By iodination of the Phe(pNH2) residue, followed by catalytic dehalogenation, the 2-(p-amino-phenylalanine) analogue is labelled with tritium at a specific radioactivity of 16 Ci/mmol. It can be converted into the tritium-labelled 2-(p-azidophenylalanine) analogue without loss of binding affinity for vasopressin receptors.