Anandamide and the metabolically stabler analogs, (R)-1'-methyl-2'-hydroxy-ethyl-arachidonamide (Met-AEA) and N-(3-methoxy-4-hydroxy-benzyl)-arachidonamide (arvanil), are CB1 cannabinoid and VR1 vanilloid receptors agonists. We synthesized dimethylheptyl-arvanil (O-1839) and six other AEA analogs obtained by addition of either a hydroxy, cyano, or bromo group on the C-20 atom of 1,1'-dimethylpentyl-Met-AEA (O-1811, O-1812 and O-1860, respectively) or 1,1'-dimethylpentyl-arvanil (O-1856, O-1895 and O-1861, respectively). The compounds were tested for their (i) affinity for CB1 and CB2 receptors, (ii) capability to activate VR1 receptors, (iii) inhibitory effect on the anandamide hydrolysis and on the anandamide membrane transporter, and (iv) cannabimimetic activity in the mouse 'tetrad' of in vivo assays. O-1812 is the first ligand ever proven to be highly (500- to 1000-fold) selective for CB1 vs both VR1 and CB2 receptors, while O-1861 is the first true "hybrid" agonist of CB1/VR1 receptors and a compound with potential therapeutic importance. The activities of the seven compounds in vivo did not correlate with their activities at either CB1 or VR1 receptors, thus suggesting the existence of other brain sites of action mediating some of their neurobehavioral actions in mice.