Breeding structure of Glossina morsitans submorsitans Newstead was evaluated by using genetic markers in mitochondrial DNA where diversity was scored at two loci in five natural populations from The Gambia and two populations in Ethiopia (form ugandensis Vanderplank), countries separated by c. 5450 km. Twenty six haplotype combinations were found, of which 17 were shared among two or more populations. Nine haplotypes were found in The Gambia and 23 haplotypes in Ethiopia. There were 12 unique haplotypes. Only six haplotypes were shared between the two countries. Populations in The Gambia (he = 0.26 +/- 0.04) showed less than a third of the diversity of populations in Ethiopia (he = 0.84 +/- 0.03). This suggests recovery from an earlier reduction in population. In a nested analysis of molecular variance of haplotype frequencies, 65% of the variance was due to differences within populations, 34% to differences between populations grouped by country, and only 1% was due to differences among populations within countries. In terms of gene flow, the fixation index FST = 0.35, which leads to an estimate by Wright's island model of less than one reproducing migrant per generation exchanged between the eastern and western submorsitans populations. Nei's genetic similarity measure showed a deep division between Gambian and Ethiopian populations.