Phenotypic and molecular methods were used to identify and compare the strain composition of three industrial dairy starters used for the manufacture of viili. Preliminary differentiation was made by phenotypic methods. Genotypic differentiation was carried out using polymerase chain reaction (PCR) and further characterization at strain level by pulsed-field gel electrophoresis (PFGE). The isolates could be assigned as acid-producing Lactococcus lactis strains of both lactis and cremoris subspecies, and aroma producers, identified as L. lactis subsp. lactis biovar diacetylactis and Leuconostoc mesenteroides. PCR analysis discriminated between the lactococcal subspecies, and cluster analysis of the digestion patterns of PFGE analysis revealed different genotypes in each subspecies. Each Leuconostoc-genotype seemed to be specific to only a single starter mix. The work proved that in addition to L. lactis subsp. lactis biovar diacetylactis and Leuc. mesenteroides subsp. cremoris, commercial viili starters of traditional origin may contain (i) only L. lactis subsp. cremoris, (ii) both L. lactis subsp. cremoris and L. lactis subsp. lactis as a minority, and - as a new discovery - (iii) only L. lactis subsp. lactis. The results obtained give an overview of the microbial population of viili starters and can be exploited in the development of optimized starter cultures for industrial-scale manufacture of viili.