Phosphorylmuramyl peptides of the formula ##STR1## are immuno-potentiating. In the formula, R.sub.1 represents optionally substituted alkyl or aryl, R.sub.2, R.sub.4, R.sub.6 and R.sub.7 represent, for example, hydrogen, R.sub.3 represents hydrogen or lower alkyl, R.sub.5 represents, for example, hydrogen, lower alkyl, hydroxy-lower alkyl, amino-lower alkyl, cycloalkyl, cycloalkyl-lower alkyl, aryl or aralkyl, or nitrogen-containing heterocyclyl or heterocyclyl-lower alkyl, and one of the radicals A.sub.1 and A.sub.2 represents a radical of the formula (II) ##STR2## In the formula (II), T represents NH or O, Y represents an optionally substituted alkylene group, which may also be interrupted by one or two oxycarbonyl and/or iminocarbonyl groups, and W represents an aliphatic radical or a cycloalkyl or cycloalkenyl radical having more than 6 carbon atoms. The other of the radicals A.sub.1 and A.sub.2 represents free or etherified hydroxy, amino, lower alkylamino or aminocarbonyl-lower alkylamino.