Composition Vector Tree (CVTree) implements a systematic method of inferring evolutionary relatedness of microbial organisms from the oligopeptide content of their complete proteomes (http://cvtree.cbi.pku.edu.cn). Since the first bacterial genomes were sequenced in 1995 there have been several attempts to infer prokaryote phylogeny from complete genomes. Most of them depend on sequence alignment directly or indirectly and, in some cases, need fine-tuning and adjustment. The composition vector method circumvents the ambiguity of choosing the genes for phylogenetic reconstruction and avoids the necessity of aligning sequences of essentially different length and gene content. This new method does not contain 'free' parameter and 'fine-tuning'. A bootstrap test for a phylogenetic tree of 139 organisms has shown the stability of the branchings, which support the small subunit ribosomal RNA (SSU rRNA) tree of life in its overall structure and in many details. It may provide a quick reference in prokaryote phylogenetics whenever the proteome of an organism is available, a situation that will become commonplace in the near future.