The fungal cell wall is unique among eukaryotes and therefore it forms an ideal target for the development of novel antifungal drugs. Fungal cell morphology and integrity depend on a cell-surrounding wall, which is composed of glycoproteins and polysaccharides. Disrupting enzymes that are involved in cell-wall biosynthesis may lead to inviable cells. For the development of polysaccharide-targeted fungicides, understanding the chemical structure and biosynthesis of cell-wall polysaccharides is essential. In this thesis, the chemical structure of cell-wall alpha-glucan is described. Analysis of alpha-glucan isolated from the model yeast Schizosaccharomyces pombe showed that it consisted of two covalently-linked building blocks. In contrast, the same polysaccharide from an alpha-glucan synthase mutant having aberrant cell morphology consisted of a single building block only. It is suggested that a single enzyme is involved in synthesis and coupling of alpha-glucan building blocks. It is further suggested that alpha-glucan biosynthesis might be initiated by a primer oligosaccharide. alpha-Glucan from S. pombe spore walls was also composed of a single alpha-glucan monomer, indicating that two mechanisms for alpha-glucan biosynthesis may exist. When analyzing alpha-glucans from a number of ascomycetous and basidiomycetous fungi, both dimeric and monomeric alpha-glucan structures were identified, indicating that the two biosynthetic mechanisms may be conserved in evolution.