Statistical and molecular genetic methodologies were used to determine the genetic variability within the Canadienne (CN), Holstein (HO), Jersey (JE) and Brown Swiss (BS) breeds of cattle and to determine the genetic distance among them. The results were intended to provide specific information to aid in the characterization and conservation of rare breeds of livestock in Canada. An analysis of the pedigrees of each breed showed that the level of inbreeding in 1994 ranged from 0.68 to 4.8%. Sixty-one and 41% of animals in the CN and HO bull populations, respectively, were being sired by only ten bulls. The average effective population size in the CN breed, 86, and the number of annual registrations, 388, were sufficiently low to characterize the CN breed as endangered. Genotyping 20 distantly related animals in each breed for 15 microsatellites and computing genetic distance estimates using Nei's standard genetic distance, the delta mu squared genetic distance and the Rst genetic distance formulae showed that the distance between individual breeds was significantly different from zero. Though not significant, CN cattle tended to be most closely related to HO and BS cattle, whereas the genetic distance between BS and HO cattle tended to be smallest. In contrast, the JE breed tended to be the most genetically distant among the breeds examined. An examination of the degree of sequence divergence in the D-loop region of mitochondrial DNA in 49 animals and a phylogenetic analysis, using a subset of the data, showed that the four breeds were not evolutionarily distinct. All four grouped together when a strict consensus tree was generated. Intra-breed variability in the D-loop sequence proved to be high for all breeds except the BS. The CN and BS as well as the BS and HO breeds showed the lowest degree of inter-breed variability. The variability seen between CN and JE cattle tended to be greatest among the four breeds.