As for other chronic viral diseases, quantification of hepatitis delta virus (HDV) loads may be useful for patient management. We describe a one-step quantitative reverse transcription-PCR assay that is reliable and automatable and meets the regulatory authorities' standards for accurate quantification of the major HDV genotypes. It includes an internal control and uses in vitro-transcribed RNAs as standards. Its linearity range is 500 to 1.7 × 10(11) copies/ml, its sensitivity is around 150 copies/ml, its repeatability is around 15%, and its reproducibility is below 0.25 log(10) copies/ml.