Tagging of two cell wall mannoproteins, Cwp1p and Cwp2p, in Saccharomyces cerevisiae with the green fluorescent protein from Aequorea victoria resulted in incorporation of fluorescent fusion proteins into the cell wall. Both living cells and isolated cell walls became brightly labeled. Intriguingly, the incorporation patterns of both fusion proteins differed. Western analysis of enzymatically released fusion proteins showed that they were covalently linked to the β-1,6-glucan part of the cell wall. Removal of the glycosylphosphatidyl-inositol anchor signal sequence of the green fluorescent protein-cell wall protein fusion proteins resulted in secretion of the proteins into the culture medium. These results indicate that green fluorescent protein-cell wall protein fusion proteins can be used as a convenient fluorescent marker to study the incorporation of specific cell wall proteins and the control mechanisms involved.