Flocculation is an important property of some yeast strains, which involves a technological improvement in different fermentative processes. In this research we have determined that flocculation ability is a property that is present in the natural flora Saccharomyces cerevisiae from the Denominacion de Origen (D. O.) Vinos de Madrid, although it has been found at low frequency. We have detected differences in the geographical distribution of flocculent strains among the three viticultural areas (Arganda, San Martin de Valdeiglesias y Navalcarnero) belonging to this D. O.; most of the flocculent strains were isolated from the middle and latest stages of the spontaneous alcoholic fermentation of musts. The assay method and flocculation capacity of yeast strains have also been evaluated, being detected evidences about the influence of the culture medium in both, expression and intensity of the flocculating character. Moreover, it has been studied the capacity of flocculent ²strains to form other cellular aggregation types. (We advise you to read the entire article. Original title: Ecological study and flocculation of yeasts from the Denomination of Origin Vinos de Madrid).