Ethanol produces supersensitivity of striatal delta-opiate receptor sites labeled by [3H]DADLE and [3H]etorphine. The impairment may be ascribed to the diminished enkephalin release detected in rat striatum after chronic ethanol consumption. On the contrary, a lower affinity of striatal mu-opiate receptors results after same ethanol exposure. In fact, the Kd values of [3H]Met-enkephalin and [3H]DHM are enhanced when measured in striata of ethanol-dependent rats. The diverse sensitivity of the various classes of opiate receptors to ethanol may be ascribed to different ethanol effects on enkephalinergic transmission.