Molecular techniques have become regular in clinical practice, becoming the basic tool in diagnosing infections, analyzing their natural histories, as well as it has become a significant marker in choosing therapeutical procedures. Correlation was shown between HBV-DNA viral load and dynamics of clinical progression of HBV infection. The appearance of HBV-DNA in patients successfully treated, precedes other markers of the loss of therapeutical control. As a result, only routine, systematic viraemia monitoring in course of therapy and analysis of mutatating HBV appearance optimize therapeutic procedures. Results of the RNA quantitative examinations and genotypes in HCV infected are the basis for the length of therapy. They are routinely performed during the period of treatment to predict its efficiency (RVR, cEVR, pEVR, EOT and SVR).