The anti-idiotype approach is based on the assumption that an antibody specific for a receptor-binding domain of a ligand could be structurally related to the receptor, Therefore, a structural mimic of a receptor-binding domain, selected with an anti-ligand antibody, might be a functional substrate for the receptor. This hypothesis was addressed here by generating antibodies recognizing the Rev-nuclear export signal (NES), A functional NES is required for active export, presumably by interacting directly or indirectly with the nuclear pore complex, Anti-NES antibodies were used to isolate RNA mimics of the NES peptide from combinatorial RNA libraries. The RNA-mimics are exported actively, block Rev-dependent export of a reporter RNA, and inhibit cap-dependent U1 snRNA export in Xenopus oocytes, properties previously reported for NES-peptide conjugates.