Abstract: Compounds of the formula ##STR1## in which R.sub.1 represents hydrogen or acyl, X.sub.1 represents an optionally N-alkylated amino acid residue that is bonded N-terminally to R.sub.1 and C-terminally to X.sub.2, X.sub.2 represents an optionally N-alkylated amino acid residue that is bonded N-terminally to X.sub.1 and C-terminally to the group --NR.sub.2 --, R.sub.2 represents hydrogen or lower alkyl, R.sub.3 represents hydrogen, alkyl, cycloalkyl, aryl-lower alkyl or aryl, R.sub.4 represents hydroxy or etherified or esterified hydroxy, R.sub.5 represents alkyl, cycloalkyl, aryl-lower alkyl or aryl, and R.sub.6 represents free or substituted amino or substituted hydroxy, and salts of such compounds having salt-forming groups inhibit the blood pressure-increasing action of the enzyme renin and can be used as anti-hypertensives.

Abstract: Compounds of the formula ##STR1## in which R.sub.1 represents hydrogen or acyl, X.sub.1 represents an optionally N-alkylated amino acid residue that is bonded N-terminally to R.sub.1 and C-terminally to X.sub.2, X.sub.2 represents an optionally N-alkylated amino acid residue that is bonded N-terminally to X.sub.1 and C-terminally to the group --NR.sub.2 --, R.sub.2 represents hydrogen or lower alkyl, R.sub.3 represents hydrogen, alkyl, cycloalkyl, aryl- lower alkyl or aryl, R.sub.4 represents hydroxy or etherified or esterified hydroxy, R.sub.5 represents alkyl, cycloalkyl, aryl-lower alkyl or aryl, and R.sub.6 represents free or substituted amino or substituted hydroxy, and salts of such compounds having salt-forming groups inhibit the blood pressure-increasing action of the enzyme renin and can be used as anti-hypertensives.

Abstract: Tetrapeptides of the formula I, ##STR1## in which R.sup.1 represents hydrogen or acyl, R.sup.2 represents alkyl or aralkyl, R.sup.3 represents free or functionally modified hydroxy, R.sup.4 represents free or substituted amino or free or etherified hydroxy, and -Pro-, -Phe- and -His- respectively represent the bivalent radicals of the amino acids proline, phenylalanine and histidine or the (D)-isomers thereof, salts of such compounds having salt-forming groups, and processes for their manufacture.The compounds inhibit the action of the enzyme renin and can be used as antihypertensives and for the treatment of cardiac insufficiency.