Grape proteins aggregate in white wine to form haze. A novel method to prevent haze in wine is the use of haze protective factors (Hpfs), specific mannoproteins from Saccharomyces cerevisiae, which reduce the particle size of the aggregated proteins. Hpf1p was isolated from white wine and Hpf2p from a synthetic grape juice fermentation. Putative structural genes, YOL155c and YDR055w, for these proteins were identified from partial amino acid sequences of Hpf1p and Hpf2p, respectively. YOL155c also has a homologue, YIL169c, in S. cerevisiae. Comparison of the partial amino acid sequence of deglycosylated-Hpf2p with the deduced protein sequence of YDR055w, confirmed five of the 15 potential N-linked glycosylation sites in this sequence were occupied. Methylation analysis of the carbohydrate moieties of Hpf2p indicated that this protein contained both N- and O-linked mannose chains. Material from fermentation supernatant of deletion strains had significantly less activity than the wild type. Moreover, YOL155c and YIL169c overexpressing strains and a strain overexpressing 6xHis-tagged Hpf2p produced greater haze protective activity than the wild type strains. A storage trial demonstrated the short to midterm stability of 6xHis-tagged Hpf2p in wine.