The chemically reactive groups of [8-arginine]vasotocin (AVT) are the a-amino group in position 1, the phenolic hydroxyl group of the tyrosyl residue in position 2, and the side-chain functional group of the basic amino acid residue in position 8. Acylation or alkylation of any of these chemically reactive groups yields hormone analogues with sharply diminished biological activities in most assay systems. Since none of the chemically reactive groups in the native AVT (or other neurohypophyseal hormone) sequences is a suitable chemical port for acylation with affinity ligands and reporter groups, we have undertaken the rational design of AVT analogues in which a residue capable of being acylated has been incorporated into points of the AVT structure where structural modifications are expected to have as little effect as possible on biological activity. Empirical structure-activity relationships among neurohypophyseal hormone analogues as well as conformational models in solution and in the crystalline state suggest that positions 4 and 7 are likely points for the introduction of acylation ports. We have previously synthesized an analogue of [l-desamino]AVT (dAVT) with a lysyl residue in position 4 ([4-lysine]dAVT) and demonstrated that acylation of the side chain of this residue yields useful reporter and photoaffinity analogues. We now report the synthesis of the corresponding analogue with a lysyl residue in position 7 ([7-lysine]dAVT), which also yields potent acyl derivatives suitable for affinity ligands and photoaffinity ligands.