PNA oligomers are promising candidates as DNA probes on account of their very high DNA binding power, but they generally require an appropriate electrochemically or spectroscopically active marker. This paper describes the systematic electrochemical characterization of two newly synthesized PNA monomers, derivatised with one or three active ferrocene groups, and of their precursors. Our monomers show high electrochemical activity in spite of their bulkiness; moreover, the systematicity of our investigation affords an interesting analysis of the role of the molecular structure, the degree of functionalization and the working solvent on the electrochemical activity of the organometallic site. (c) 2005 Elsevier B.V. All rights reserved.