Résumé : Three cyclic disulfide analogs related to somatostatin, d‐Phe1 ‐Cys2‐Tyr3‐d‐Trp4‐Lys5‐Thr6‐Xxx7‐Thr8NH2 (where Xxx =l‐Pen 1; l‐Cys 3; or d‐Pen 4) were examined in DMSO‐d6 by one‐ and two‐dimensional proton n.m.r. spectroscopy in order to analyze the conformational influence of the position‐7 residue on the 20‐membered disulfide ring. From these studies it was concluded that all three analogs maintain a β II turn solution conformation for the core tetrapeptide‐Tyr3‐d‐Trp4‐Lys5‐Thr6‐. However, the disulfide conformation differs in the analogs, with 1 and 3 having a left‐handed and 4 a right‐handed disulfide chirality. Copyright © 1988, Wiley Blackwell. All rights reserved