The invention provides polypeptides of the formula, wherein A is Tyr or substituted Tyr, B is, for example, -Gly-, -(D)-Ala-, or -(D)-Met-, D is Phe or substituted Phe, E is, for example, -Leu-, -Nle-, -Nva-, -Ile- or -Val-, and F is -NR.sub.7 CHR.sub.8 CH.sub.2 OR.sub.3 ', wherein, for example, R.sub.3 ' may be hydrogen or alkyl--CO--, R.sub.7 is hydrogen or alkyl and R.sub.8 is alkyl, which compounds possess pharmacological activity, for example, analgesic activity.