The determination of viral RNA sequences from different areas of the genome has now become routine and numerous laboratories around the world have this capability; this has added exponentially to the number of DENV samples available for comparison in GenBank. The comparison of these nucleotides and their encoded amino acids can be done with sophisticated computer algorithms that can tell us much about the rates and sites of mutation or evolution in the viral genome. These data can then be matched with patient viral loads, diagnoses, outbreak characteristics and transmission distribution, to look for specific associations. The RT-PCR technique has allowed for the enzymatic amplification of these sequences from very small amounts of viral RNA from almost any type of tissue but many researchers have now avoided virus isolation and characterization, thus introducing mistakes in some of the banked information (e.g., from amplification, sequencing, or cloning artifacts) and without information on viability or antigenicity. Therefore, it is also important to have access to classic virology techniques, especially if one is to derive information about virus phenotype.