The cyclic delta opioid agonist [p-I-Phe4]DPDPE, 1, was conjugated to mono-6-amino-permethyl-beta-cyclodextrin at the C-terminus to improve the bioavailability of 1. In the rat brain binding assay, the conjugate 8 showed an IC50 = 134 nM vs. a delta ligand and IC50 > 10 muM at the mu receptor, making it less potent and selective than 1. However, 8 shows antinociceptive properties (i.v.) in the mouse tail flick test and prolonged activity.