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Alternaria solani produced two homogeneous exocellular polysaccharide fractions when grown in shake culture with fructose as the carbon source and the NH4NO3 concentration of the medium 1.7 g/l. Chromatographic techniques indicated that fraction I contained glucose, galactose, and glucosamine in a 2.4:1:1 ratio whereas fraction II contained glucose, galactose, and mannose in a 6.4:1:1.2 ratio. Fraction I was found at levels seven times greater than II. Total polysaccharide produced was 1.8% of the dry weight of the mycelium and 1.2% of the available carbohydrate.Growth and polysaccharide production were greatest with fructose as the carbon source. Decreasing levels of growth occurred with mannitol, glucose, and sucrose, respectively. Exocellular polysaccharides were not detected with mannitol as carbon source. At 10 days, growth on fructose is maximum at NH4NO3 concentrations of 1.5 to 2.5 g/l, but exocellular polysaccharide production is maximum at 0.8 g/l. When produced on a medium of 2.0 g/l NH4NO3 the nitrogen content of I is double that when the medium is 0.8 g/l NH4NO3. In addition the ratio of I to II is about four times greater.