Accurate and rapid diagnosis of human cytomegalovirus (HCMV) disease in immunocompromised patients has remained as a challenge. Quantitative competitive PCR (QC-PCR) methods for detection of HCMV in these individuals have improved the positive and negative predictive values of PCR for diagnosis of HCMV disease. In this study we used QC-PCR assay, using a co-amplified DNA standard, to quantitate the HCMV glycoprotein B (gB) gene in different samples. A DNA internal standard (IS) was designed by replacing HCMV primer binding site at 5' ends of primers that amplifies a 156-bp fragment of lambda genome, and a 200 bp amplicon was produced. Two DNA fragments of 257 bp wild type and 200-bp (IS) were co-amplified with the same oligonucleotide primer sets, analyzed by gel electrophoresis and used for construction of a standard curve. From this, the copy number of the gB gene present in different samples could be determined. Co-amplification with 1,000 copies of IS, allowed quantitation of 10-100,000 of HCMV DNA in a single PCR. This rapid assay avoids using radioactive components and other less efficient quantitative systems. It has the potential for early identification of patients at high risk of development of HCMV disease, and is useful for therapeutic monitoring. Iran. Biomed. J. 9 (4): 187-191, 2005