Based on [1-(1-mercaptocyclohexaneacetic acid),2-(O-ethyl-D-tyrosine),4-valine]-8-arginine-vasopressin as a model, five new analogues of arginine-vasopressin (AVP) were designed and synthesized. Four of them have in position 1 a large lipophilic substituent, whereas the fifth contains pchloro-D-phenylalanine at position 2. We found that the anti-antidiuretic potency with 1-mercapto-4-methycyclohexaneacetic acid is higher than with 1-mercaptocyclohexaneacetic acid (model peptide) in position 1 and this analogue is among the most potent antagonists of the antidiuretic response to AVP known to date. Upon further increase of the size of substituents, antagonistic potency was significantly decreased or totally eliminated. As for the substitution of p-chloro-D-phenylalanine in position 2, we conclude that this modification leads to substantial decrease of the V2 antagonistic potency.