Random amplified polymorphic DNA (RAPD) markers were used to quantify the genetic diversity and its distribution in liver fluke, Fasciola hepatica recovered from seven definitive hosts belonging to Ukrainian and Armenian cattle populations. Five oligonucleotide primers produced complex and highly variable patterns of amplified DNA in F. hepatica. Intra- and interpopulation genetic variability of adult parasites was analyzed on the base of polymorphic and monomorphic reproducible bands. Genotypic diversity calculated by Shannon's indices showed that the majority of variance occurred within, rather then between hosts and was also greater within than between populations. Analysis of molecular variance was used to test the significance of genetic differentiation within and between populations of worms. Of total gene diversity, 86.54% were partitioned within hosts, 8.17% of variability accounted by the differences among hosts/within populations and 5.3% of variation by the differences between populations. These results suggest that each individual cow is infected by numerous genetically different parasites. Migration of definitive hosts and other factors influencing the distribution of liver fluke RAPD variability are discussed.