Abstract: Compounds of formula (I): ##STR1## [in which: R.sup.1 is heterocyclic group having 5 or 6 ring atoms, or --NR.sup.7 R.sup.8, where R.sup.7 is alkyl and R.sup.8 is optionally substituted phenyl, optionally substituted phenylalkyl or cycloalkyl; R.sup.2 is optionally substituted phenyl or naphthyl; R.sup.3 is thiazolyl; R.sup.4 is cyclohexyl or isopropyl; R.sup.5 is alkyl; and R.sup.6 is alkyl] and salts thereof have renin-inhibitory and, hence, hypotensive activities and are of value in the diagnosis and treatment of hypertension induced by failures in the renin-angiotensin system. They may be prepared by reacting together appropriate amino acids or derivatives thereof.

Abstract: Oligopeptides of formula (I): ##STR1## where R.sup.1 -R.sup.5 are various organic groups, and A represents a group of formula --NH-- or --(CH.sub.2).sub.n --, in which n represents an integer of from 1 to 3, have renin-inhibitory activity and are particularly suitable for oral administration. They may be prepared by condensing their component amino acids or lower oligopeptides using conventional peptide synthesis reactions.

Abstract: Compounds of formula (I): ##STR1## A is a carbon-carbon bond or C.sub.1 -C.sub.3 alkylene; B is imino group or C.sub.1 -C.sub.2 alkylene; R.sup.1 is C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, heterocyclic or optionally substituted amino; R.sup.2 is optionally substituted phenyl or optionally substituted naphthyl; R.sup.3 is thiazolyl, isoxazolyl or imidazolyl; R.sup.4 is isopropyl or cyclohexyl; R.sup.5 and R.sup.6 are C.sub.1 -C.sub.4 alkyl, or, together with the carbon atom to which they are attached, C.sub.3 -C.sub.7 cycloalkyl; R.sup.7 is hydrogen, optionally substituted C.sub.1 -C.sub.6 alkyl group; and R.sup.8 is hydrogen or C.sub.1 -C.sub.4 alkyl. These compounds have renin-inhibitory and, hence, hypotensive activities. The invention also provides a method for the treatment or prophylaxis of hypertension induced by failures in the renin-angiotensin system.