Eight ovine microsatellite loci were amplified in 40 to 50 unrelated individuals from six sheep populations representing five breeds: Romney, Border Leicester, Suffolk, Awassi, and both Australian and New Zealand Merino. For all of the microsatellite loci analyzed, there were highly significant differences in allele frequencies between samples from the different breeds. The allele frequencies generated can be used to determine the breed of an individual, given that it comes from one of the above breeds, to a high degree of accuracy. There were also some alleles that were found in only one breed, although these alleles were at such low frequencies that they are unlikely to be useful as markers for a breed. Genetic distances between breeds were obtained using Nei's formula to construct a phylogenetic tree. The tree grouped the Merino's in one branch and the Border Leicester, Suffolk, and Romney in another branch, while the Awassi, which was used as an outgroup, had its own branch. Using Nei's unbiased genetic distance formula to calculate the time of divergence of the British breeds from the Merino and the time of divergence between the Australian and the New Zealand Merino, we obtained t = 1094 and t = 227 years, respectively. Microsatellite genotyping in sheep appears to provide a useful tool for examining the evolutionary relationships between breeds.