Method of inducing analgesia

A method for inducing analgesia is a mammal in need thereof, which comprises the peripheral administration into said mammal of an amount effective to induce analgesia of a compound having the formula:

• ##STR3## wherein R.sup.1 is ##STR4## wherein R.sup.3 is hydrogen, chloro, methyl, nitro, hydroxy or amino and n is 0 or 1 and
• R.sup.2 is lower alkyl of 1 to 6 carbon atoms, hydroxy lower alkyl, alkylthioalkyl, carboxamido-lower alkyl or carboxy lower alkyl, provided that when R.sup.1 is benzyl and R.sup.2 is isobutyl the configuration of the compound is 2S,3R,2'R), (2S,3S,.alpha.'S) or (2S,3S,2'R) and the pharmacologically acceptable salts thereof.