Prior work in our laboratory has identified putative subtypes of delta (delta cx-1, delta cx-2, delta ncx-1, delta ncx-2) and kappa 2 (kappa 2a and kappa 2b) receptors. Previous studies showed that chronic (three day) i.c.v. administration of antisense oligodeoxynucleotide to the cloned delta opioid receptor selectively decreased [3H][D-Ala2,D-Leu5]enkephalin binding to the delta ncx site, not the delta cx-2 site. The present study extends this work by demonstrating that delta antisense DNA selectively affects the delta ncx-2 site sparing the other putative delta receptor subtypes and kappa 2 receptor subtypes. This selectivity is not due to anatomically specific effects of delta antisense DNA since autoradiograms show that delta binding is reduced in all regions of the brain after chronic i.c.v. administration of delta antisense DNA. These data strongly suggest that the delta cx-1, delta cx-2, delta ncx-1, kappa 2a and kappa 2b binding sites are different proteins than the delta ncx-2 binding site, which, based on its sensitivity to delta antisense DNA, is synonymous to the cloned delta opioid receptor. Viewed collectively, these data suggest that administration of delta antisense DNA, and by extension other receptor-selective antisense DNA, is a powerful approach to distinguishing between postulated receptor subtypes.