Anti-aggregatory peptides

A compound of formula (II):

• ##STR4## (II) wherein:
• A' is a D- or L-amino acid chosen from Arg, HArg, (Me.sub.2)Arg, (Et.sub.2)Arg, Ala, Gly, His, Abu, Lys or an .alpha.-R' substituted derivative thereof, or Pro;
• B' is an .alpha.-R' substituted derivative of D- or L-Arg;
• C' is a D or L amino acid chosen from Tyr, (Alk)Tyr, Phe, (4'W)Phe, HPhe, Phg, Trp, His, Ser, (Alk)Ser, Thr, (Alk)Thr, (Alk)Cys, (Alk)Pen, Ala, Val, Nva, Met, Leu, lie, Nle or Nal, or an .alpha.-R' substituted derivative thereof;
• W is halogen or Alk;
• Y is NR.sub.1 R.sub.2 or OR.sub.3 ;
• R.sub.1 and R.sub.2 are each independently H, Alk or (CH.sub.2).sub.p Ph;
• R.sub.3 is Alk, (CH.sub.2).sub.p Ph or H;
• X is R.sub.4 R.sub.5 N or H;
• R.sub.4 is H or Alk;
• R.sub.5 is H, Alk, HCO, AlkCO, PhCH.sub.2 or Ph(CH.sub.2).sub.q CO;
• R' is Alk or PhCH.sub.2 ;
• Z.sub.1 is a D- or L-isomer of Cys, Pen or APmp;
• Z.sub.2 is a D- or L- isomer of Cys, Pen or APmp;
• q, m and n are independently 0 or 1;
• and
• p is 0, 1, 2or 3;
• or a pharmaceutically acceptable salt thereof.