Aims: To characterize and analyze the flocculation phenomenon of Kloeckera apiculata mc1 from Agentinian wine to understand the cell-cell interaction pattern. Methods and Results: Kloeckera apiculata mc1 possess intense cell-cell interactions in MYPG medium (0.5% malt extract, 1% yeast extract, 2% glucose, 2% peptone), pH 5.5 by shaking at 25degreesC. Optimum flocculation is observed at pH 4.5 in the presence of 3 mmol l(-1) Ca2+ . The flocculation is induced by peptone and malt extract and not by yeast extract and is reversed by 50 mmol l(-1) galactose or lactose. The flocculation is highly susceptible to pronase, chymotrypsine and proteases types IV and XXVII and is partially resistant to trypsin. The electronic microscopy shows that the cells are attached to each other along their sides by fine hair-like threads. Conclusions: The mechanism of flocculation of K. apiculata mc1 is mediated by protein-carbohydrate interaction, stabilized by Ca2+ . Significance and Impact of the Study: The use of selected pure yeast inocula of known ability is preferred to wine elaboration, therefore the indigenous flora must be avoided and the flocculation of K. apiculata could be an economic method to do it.