Compounds having kappa opioid agonist activity, compositions containing them and 5 method of using them as analgesics and pruritic agents are provided.The compounds of formulae I, II, III and IV have the structure: ##STR00001## wherein X, X.sub.4, X.sub.5, X.sub.7, X.sub.9; R.sub.1, R.sub.2, R.sub.3, R.sub.4; and Y, Z and n are as described in the specification.