G-DNA is a polymorphic family of quadruple helical nucleic acid structures containing guanine tetrad motifs [G-quartets; Willlamson, J. R., Raghuraman.M.K. and CechJ.R. (1989) Cell 59, 871–880; Williamson. J. R. (1993) Proc. Natl. Acad. Scl . USA 90, 3124–3124]. Guanine rich oligonucleotides that are self-complimentary, as found in many telomeric G-strand repeat sequences, form G-DNA in the presence of mono-valent and/or divalent metal cations. In this report we use the atomic force microscope (AFM) to explore the structural characteristics of long, linear polymers formed by the telomeric oligonucleotide d(GGGG TTGGGG) in the presence of specific metal cations. In the AFM these polymers, termed G-wires, appear as filaments whose height and length are determined by the metal ions present during the self-assembly process. The highly ordered, controllable serf-assembly of G-wires could provide a basis for developing advanced blomaterials.