Electrochemical single nucleotide polymorphisms (SNPs) detection was investigated on gold surface modified with 16-base-pair duplex DNAs. In these duplexes, probe DNAs consisted of complementary sequences for target DNAs and a series of ferrocene-diamidopyridine conjugates as an electrochemically active moiety. Regardless of isomeric structures in the conjugates, all the DNA probes showed electrochemical discrimination between fully matched DNAs and SNPs. A detailed comparison was carried out for these probes. [DOI: 10.1380/ejssnt.2005.393]