Molecular biology techniques are applied for the diagnosis of meningoencephalitis due to herpesviruses, enteroviruses or polyomaviruses, for the diagnosis of human cytomegalovirus, human parvovirus B19, varicella-zoster virus and rubella virus infections occurring during pregnancy, for the diagnosis and the management of retrovirus infections (HIV and HTLV) and of hepatitis (HBV and HCV), for papillomavirus typing and to detect a link between virus and clinical manifestations (cardiomyopathy or insulinodependent diabetes with coxsackievirus B: Kaposi's sarcoma with HHV 8) or to investigate an environmental contamination with viruses. These new molecular markers which are both qualitative and quantitative represent an important advance in the field of viral diagnosis research, in the monitoring of viral load during the course of infection, in the therapy control of viral disease and in the epidemiology of virus spread. Standardization and automatization are obtained using available commercial reagents and kits.