The invention relates to macrocyclic lactam derivatives of formula I ##STR1## wherein R is hydrogen or acyl; m is an integer from 4 to 9 inclusive; n is 1 or 2; p is zero, 1 or 2; X is --CONH-- or --NHCO--; Y is S, O or CH.sub.2 ; R.sub.1 is --COOH; or R.sub.1 is ##STR2## in which R.sub.2 is hydrogen, lower alkyl, aryl-lower alkyl, amino-lower alkyl, hydroxy-lower alkyl, acyloxy-lower alkyl, lower alkoxy-lower alkyl, mercapto-lower alkyl, lower alkyl-(thio, sulfinyl or sulfonyl)-lower alkyl, or carboxy-lower alkyl, R.sub.3 is hydrogen or lower alkyl, and q is zero or an integer from 1 to 5 inclusive; or R.sub.1 is ##STR3## in which R.sub.4 is hydrogen, lower alkyl, lower alkoxy, hydroxy or acyloxy, and r is 1 or 2; or R.sub.1 is ##STR4## in which s is 1 or 2; or R.sub.1 is ##STR5## in which R.sub.5 and R.sub.6 independently represent hydrogen, lower alkyl, C.sub.5 - or C.sub.6 -cycloalkyl, (hydroxy-, acyloxy or lower alkoxy-) lower alkyl, carbocyclic or heterocyclic monocyclic aryl, or (hydroxy-, acyloxy- or alkoxy-) lower alkyloxy-lower alkyl; or R.sub.5 and R.sub.6 together with the nitrogen to which they are attached represent pyrrolidino, piperidino, morpholino, piperazino or N-alkylpiperazino; and macrocyclic sulfur and oxygen containing lactam ring isomers in which a CH.sub.2 group of (CH.sub.2).sub.m in formula I is replaced by O or S, and Y represents CH.sub.2 ; and pharmaceutically acceptable prodrug esters of any above said compound with a free carboxyl group; and pharmaceutically acceptable salts of any said compounds with a free acid or basic salt forming group; pharmaceutical compositions comprising said compounds; methods for the preparation of said compounds and for the preparation of intermediates; and methods of treating disorders in mammals which are responsive to the inhibition of neutral endopeptidases by administration of said compounds to mammals in need of such treatment.