The synthesis of RNA molecules carrying acridine or quindoline residues at their 3'- and 5'-termini is reported. These conjugates are fully characterized by MALDI-TOF mass spectrometry. Modified siRNA duplexes carrying acridine or quindoline moieties were evaluated for inhibition of the tumor necrosis factor. The conjugates showed inhibitory properties similar to those of unmodified RNA duplexes in HeLa cells transfected with oligofectamine. The fluorescent properties of acridine derivatives allow direct observation of the cytoplasmatic distribution of modified siRNA inside the cells.