In order to investigate the origin of the Eastern Slavs, mitochondrial DNA (mtDNA) sequence variation was examined in Russians and Ukrainians by hypervariable segment I (HVS I) sequencing and restriction analysis of the haplogroup-specific sites. No significant differences were found for Russians and Ukrainians when compared to other Europeans - in fact, they fall within the range of gene diversity seen throughout Europe and exhibit the unimodal pattern of pairwise sequence differences. Moreover, HVS I sequences in the Russians and Ukrainians are similar or identical to those found in eastern and western European populations. Despite the small genetic distances between Europeans, phylogenetic analysis reveals a considerable heterogeneity of Eastern Slavonic populations - they do not cluster together onto a phylogenetic tree. Analysis of distribution of rare HVS I types shared between populations of Eastern Slavs and other West Eurasians has shown that Russians share rare haplotypes mainly with Germans and Finno-Ugric populations. Of these, subhaplogroup H1 sequence types, which are defined by different combinations of nucleotides 16192T, 16294T, 16304C, 16311C and 16320T, are found predominantly in common between Russians and German-speaking populations. The data obtained allow us to conclude that the Slavonic migrations in early Middle Ages from their putative homeland in central Europe to the east of Europe were accompanied mostly by the same mtDNA types characteristic for the pre-Slavonic populations of eastern Europe.