Abstract: Novel peptides of the formula: ##STR1## wherein: A, A' and A" are each independently Gly, D-Ala, D-Leu, or D-Trp, wherein A may optionally be N-alkylated or N-acylated;B is Pro, .DELTA..sup.3 -Pro, Thz, or diMeThz;C and C' are each independently Thr, Ser, Val, or alloThr;D is Glu, Gln, Asp, or Asn;R is hydrogen, or is lower alkyl or lower acyl, substituted for one of the hydrogens on the .epsilon.-amino group of the lysyl residue;X is Cys, Ala, ABU, or Cys(Me); andY is selected from the group consisting of hydroxy, Pro, Pro-Leu, and Pro-Leu-Met, -NH.sub.2, ProNH.sub.2, Pro-LeuNH.sub.2 and Pro-leu-MetNH.sub.2 ;and the pharmaceutically acceptable salts thereof, are useful for increasing immunologic competence. Methods for preparation of the peptides are also described.