Naltrexone-derived antagonists which are highly selective for delta opioid receptors have been designed using the message-address concept. The prototypical member of this series, naltrindole 1, possesses very high affinity and selectivity for delta receptors, and a closely related benzofuran analogue, NTB 2, is a selective delta 2 antagonist. The fact that 7-benzylidenenaltrexone (BNTX) was found to be a delta 1 antagonist suggests that the conformation of the putative delta address component (phenyl group) of BNTX plays a role in modulating delta subtype selectivity.