This research was developed to track the microbial composition of raw milk obtained from twelve successive milking operations from the same farm with a special attention to lactococci, enterococci, lactobacilli and leuconostocs. Entereococci, lactobacilli and leuconostocs were detected at low levels. Lactococci represented the most abundant microflora. The dominance of Lc lactis subsp. cremoris from days 1 to 5 was followed by the dominance of Lc lactis subsp. lactis. Technological characterizations, Rep-PCR and whole-cell protein patterns analyses revealed the existence of two groups of lactococci. The first group designed as fundamental microflora included strongly acidifying strains. They were present day after day. The second group-transitory microflora was observed occasionally and was less acidifying. A major influence of the biofilms of the milking equipment was postulated to explain the stability and the composition of the fundamental microflora. The implication of these observations on natural whey starters' competition and cheese particularity is discussed.