BACKGROUND Development of the polymerase chain reaction and deoxyribonucleic acid sequencing techniques has enabled precise identification, classification and taxonomy of viruses. COMPARATIVE SEQUEENCE ANALYSIS: (Comparative sequence analysis methods can be used in medical virology for many practical purposes. They may be classified into three broad categories: I - reconstruction of genealogical relationships between individual viral isolatesfor detection and monitoring of sources, reservoirs and modes of viral transmission; II - virus genotyping, that is determination of relationships between genetic types of viruses and their phenotypic properties, which has important implications for immunoprophylaxis, therapy and prognosis of viral diseases, and III investigation of functional properties of defined viral sequences, of special importance for explanation of viral pathogenesis and design of antiviral drugs. CONCLUSIONS The combination of DNA sequencing with polymerase chain reaction following reverse transcription with the use of random primers offers a universal means for diagnosis of viral infections.