Scanning electrochemical microscopy (SECM) has been employed in the imaging of DNA microarrays fabricated on gold substrates using methylene blue (MB) as a redox-active intercalator and ferrocyanide as the SECM mediator in solution. MB intercalated between base pairs of immobilized ds-DNA is electrochemically reduced via electron transfer from the underlying gold substrate, and the product is reoxidized in solution by SECM tip-generated ferricyanide. The resulting feedback current allows a heterogeneous electron-transfer rate constant for the MB-intercalated DNA to be deduced. Moreover, DNA microarray spots can be imaged at a detection level of 14 fmol/spot for ds-DNA consisting of 15 base pairs. Microarrays prepared using 20 mu M DNA solutions are easily visualized, and the feasibility of detecting base pair mismatches is also demonstrated.