A disposable electrochemical biosensor for the detection of DNA sequences related to the human cytomegalovirus (HCMV) is described. The sensor relies on the adsorption of an amplified human cytomegalovirus DNA strand onto the sensing surface of a screen-printed carbon electrode, and to its hybridization to a complementary single-stranded biotinylated DNA probe. The extent of hybrids formed was determined with streptavidin conjugated to horseradish peroxidase. The peroxidase label was indirectly quantified by measuring the amount of the chromophore and electroactive product 2,2-diaminoazobenzene generated from the ophenylenediamine substrate. The intensity of differential pulse voltammetric peak currents resulting from the reduction of the enzyme-generated product was related to the number of target HCMV-amplified DNA molecules present in the sample, and the results were compared to those obtained with standard methods, i.e., agarose gel electrophoresis quantification and colorimetric hybridization assay in a microtiter plate. A detection limit of 0.6 amol/ml of HCMV-amplified DNA fragment was obtained with the electrochemical DNA biosensor. The electrochemical method was 23,000-fold more sensitive than the gel electrophoresis technique and 83-fold more sensitive than the colorimetric hybridization assay in a microtiter plate.