Co-flocculation is the aggregation of yeasts belonging to different genera or species. Kluyveromyces bulgaricus and Kluyveromyces lactis 5c are self-flocculent, but they can also co-flocculate with the non-flocculent yeast Schizosaccharomyces pombe 972 h(-). This co-flocculation is inhibited by D-galactose and galactose derivatives and involves the binding of a galactose-specific proteinic receptor (or lectin) of Kluyveromyces sp. to the cell wall galactomannans of S. pombe. The proteinic receptor is strongly anchored in the cell wall, it was partially purified by affinity chromatography using immobilized S. pombe galactomannans. This galactose-specific proteinic receptor does not appear to interfere in K. bulgaricus or K. lactis self-flocculation, which is mediated by another galactose-specific lectin weakly linked at the cell wall.