Substituted aryl and aliphatic amide analogues of 6-naltrexamine were synthesized and used to characterize the binding to and functional activity of human mu-, delta-, and kappa-opioid receptors. Competition binding assays showed 11-25 and 27-31 bound to the mu (K(i) = 0.05-1.2 nM) and kappa (K(i) = 0.06-2.4 nM) opioid receptors. Compounds 11-18 possessed significant binding affinity for the delta receptor (K(i) = 0.8-12.4 nM). Functional assays showed several compounds acted as partial or full agonists of delta or kappa receptors while retaining an antagonist profile at the mu receptor. Structure-activity relationship for aryl amides showed that potent compounds possessed lipophilic groups or substituents capable of hydrogen bonding. Metabolic stability studies showed that 11, 12, and 14 possessed considerable stability in the presence of rat, mouse, or human liver preparations. The ED 50 of inhibition of 10% ethanol self-administration in trained rats, using operant techniques for 11, was 0.5 mg/kg.