Tripeptides of the general formula: ##STR1## wherein the symbols R, which may be the same or different represent hydrogen or a fatty acid residue (at least one of them representing a fatty acid residue), R.sub.1 represents hydroxy, amino or alkoxy and R.sub.2 and R.sub.3, which may be the same or different, represent hydrogen, carboxy, carbamoyl or alkoxycarbonyl radical (with the proviso that R.sub.2 and R.sub.3 cannot simultaneously represent a hydrogen atom), the alanine moiety being in the L form, the glutamic acid moiety being in the D form, the lysine moiety (when R.sub.2 or R.sub.3 =a hydrogen atom) being in the L form and the 2,6-diaminopimelic acid moiety or its derivatives (when R.sub.2 and/or R.sub.3 =carboxy, carbamoyl or alkoxycarbonyl) being in the D,D, L,L, D,D/L,L (racemic) or D,L (meso) form, and salts thereof, possess immunological adjuvant and immunostimulant activity.