Abstract: There are described novel trans-2-acylaminocyclohexyloxyacyldipeptides of formula I ##STR1## wherein R.sub.1 represents --CO--R.sub.6, --SO.sub.2 --R.sub.7 or ##STR2## R.sub.6 is C.sub.1 -C.sub.18 alkyl or C.sub.1 -C.sub.18 alkoxy, R.sub.7 is C.sub.1 -C.sub.18 alkyl or an optionally substituted phenyl group,Y is .dbd.O, .dbd.S or .dbd.NH;R.sub.2 =R.sub.3 and represent --H or C.sub.1 -C.sub.12 alkyl,R.sub.4 represents --OR.sub.8 or --NHR.sub.9,R.sub.8 is --H, C.sub.1 -C.sub.8 alkyl or benzyl,R.sub.9 is --H, a straight or branched chain C.sub.1 -C.sub.18 alkyl group or benzyl group;R.sub.5 represents --OR.sub.9 or --NHR.sub.9,and novel (1R,2R)- and (1S,2S)-trans-2-acylaminocyclohexyloxyacetyldipeptides of the formulas Ia and Ib ##STR3## wherein R.sub.1 is --CO--R.sub.6, R.sub.6 is C.sub.1 -C.sub.18 alkyl,R.sub.2 is --H,R.sub.3 is --H or C.sub.1 -C.sub.12 alkyl,R.sub.4 is --OR.sub.8 or --NHR.sub.9,R.sub.8 is --H, C.sub.1 -C.sub.8 alkyl or benzyl,R.sub.9 is --H, C.sub.1 -C.sub.18 alkyl or benzyl,R.sub.5 is --OR.