Abstract: This invention is directed to an adjuvant composition in the form of an emulsion which is comprised of an emulsion-forming amount of a non-toxic tetra-polyol or of a POP-POE block polymer and an immunopotentiating amount of a muramyldipeptide of the formula: ##STR1## or a pharmaceutically acceptable salt thereof, where R and R.sub.1 are each independently H or acyl of 1 to 22 carbon atoms, R.sub.2 is optionally substituted alkyl or optionally substituted aryl, R.sub.3 is H, alkyl, or aryl, R.sub.4 is H or lower alkyl, X is L-alanyl, L-.alpha.-aminobutyryl, L-arginyl, L-asparginyl, L-aspartyl, L-cysteinyl, L-glutaminyl, L-glutamyl, glycyl, L-histidyl, L-hydroxyprolyl, L-isoleucyl, L-leucyl, L-lysyl, L-methionyl, L-ornithinyl, L-phenylalanyl, L-prolyl, L-seryl, L-threonyl, L-tyrosyl, L-tryptophanyl, or L-valyl, and Y is D-glutamine, D-isoglutamine or D-isoasparagine. This invention is also directed to a vaccine containing an antigen and an adjuvant composition of the invention.