Summary.A sensitive and reliable quantitative method based on the polymerase chain reaction (PCR) and the reverse transcription polymerase chain reaction (RT-PCR) to detect and quantify human immunodeficiency virus (HIV-1) and hepatitis B virus (HBV), respectively, was developed. The samples are co-processed together with two internal standards (calibrators). The amplicons are separated on denaturing polyacrylamide gels and co-detected and quantitated by laser induced fluorescence. HIV-1 and HBV containing biological samples, including samples from international test panels, were accurately quantitated. The procedure has proven to be a valuable tool in the quality control of biologicals such as plasma products and may serve to monitor disease progression and response to antiviral therapy.