In order to specifically direct cytotoxic agents against tumor cells bearing 6 opioid receptors, the DNA intercalating agents ellipticine and 9-OH-ellipticine were coupled by quaternarization of the pyridine nitrogen to an enkephalin modified pentapeptide through a short chemical linker. The ellipticine ring of these conjugates was shown to intercalate into DNA, with DNA affinity constants close to those of the nonconjugated ellipticines. Despite the addition of a polycyclic ring to the C-terminal amino acid, the D-Ala2 -D-LeuS -enkephalin-ellipticine conjugates bind to the opioid receptor from rat brain and NG 108-15 cells with an affinity constant close to lo* M-'. Other derivatives were synthesized as a control using a tripeptide which does not bind to the opioid receptor.