A simple and reliable method based on electrochemical technique at beta-cyclodextrin incorporated carbon nanotubes-modified electrodes (beta-CD-CNT/E) was proposed for simultaneous or individual determination of guanine and adenine. After accumulation on beta-CD-CNT/E at open circuit for 1 min, guanine and adenine produced well-defined oxidation peaks at about +0.79 and +1.09 V in pH 4.5 acetate buffer. The electrocatalytic mechanism was firstly discussed and revealed in detail from the point of the interface layer microstructure of the composite electrode. The novel modified electrode brings new capabilities for electrochemical devices by combining the advantages of carbon nanotubes and supramolecular cyclodextrins. The results demonstrated that the utility of beta-CD-CNT/E clearly provides an effective methodology for the estimations of guanine and adenine. Further, the marked electrocatalytic activity permits effective low-potential amperometric biosensing of DNA with the detection limits of 0.1 and 0.2 mu g ml(-1) for guanine and adenine, respectively. (c) 2006 Elsevier B.V. All rights reserved.