INTRODUCTIONThe Swiss Brown from Germany (German Brown) and the Austrian Swiss Brown(Montafoner) were imported after World War I to upgrade Turkish cattle for milkproduction. Pure-bred herds are maintained at government farms. These breedsand their crosses to the native cow now account for nearly 3% of the nationalherd.A primary objective of genetic conservation schemes is the maintenanceof maximum genetic variation within species. In livestock species, this can beachieved by the preservation of breeds (Hall and Bradley, 1995). The level ofgenetic differentiation among Swiss Brown subpopulations will depend on theunderlying population structure and the amount of migration between them. Thelonger the time populations have remained isolated, the greater will be the geneticdifferentiation due to genetic drift, particularly if the effective population size hasbeen small. However, the significant level of importation of Swiss Brown intoTurkey would suggest that Swiss Brown herds may be becoming genetically morealike.Very little is known about genetic diversity and population structure ofSwiss Brown cattle in Turkey. The objectives of this study were to determinepopulation structure and to assess the level of genetic differentiation betweensubpopulations of some Swiss Brown in Turkey by using blood proteinpolymorphisms.