Some strains of Saccharomyces cerevisiae form a biofilm called a "flor" on the surface of wine after ethanolic fermentation, but the molecular mechanism of flor formation by the wild-type flor strain involved in wine making is not clear. Previously, we found that expression of the C-terminally truncated form of NRG1 (NRG1(1-470)) on a multicopy plasmid increases the hydrophobicity of the cell surface, conferring flor formation on the non-flor laboratory strain. Here we show that in Ar5-H12, a wild-type flor haploid strain, flor formation is regulated by NRG1(1-470). Moreover, the disruptant of the wild-type flor diploid strain (Deltaflo11/Deltaflo11) show a weak ability to form the flor. The expression of FLO11 is always high in the wild-type flor strain, regardless of carbon source. Thus FLO11 is primary factor for wild-type flor strains. Furthermore, the disruptant (Deltaflo11) shows lower hydrophobicity of cell surface than the wild type. However, the hydrophobicity of the wild-type flor strains grown in ethanol medium was much higher than those grown in glucose medium. These results indicate that cell surface hydrophobicity is closely related to flor formation in wild-type flor yeasts.