Users may upload their own genomic sequences to the CVTree web server. All sequences of one and the same organism should be included in one FASTA file. The file name (without extension) will be displayed as the organism name in the trees. For user's convenience, sequences for a number of organisms may be wrapped Figure 1 . Two-step implementation of CVTree. CVTree implements a two-step strategy to produce phylogenetic trees. In the first step, CVTree reads in each genome sequence and counts the frequency of all K-tuples. Then the CV of each organism is calculated and dumped to the hard disk (CV files). In the second step, CVTree calculates the dissimilarity matrix from the correlation between CVs. Finally, the tree files are generated by the neighbor-joining program in PHYLIP package.