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Phormidium 94a, a cyanobacteria that produces extracellular polymeric substances (EPS), was isolated from arid soils of Mexico. Microscopic localization, using histochemical techniques like the Toluidine blue technique, was done in order to demonstrate the presence of EPS. Acetone was added to precipitate the EPS. In this study we characterized the EPS by GC, HPLC, and IR techniques. The highest fraction of EPS had a molecular weight of 2,000 kDa. The sugar composition was galactose, mannose, galacturonic acid, arabinose, and ribose in the three main fractions, and the sugar ratio found was different in each fraction. The low EPS concentrations had a Newtonian behavior, when the concentrations were increased, the behavior changed to pseudoplastic. The EPS rheulogical behavior is similar to low viscosity arabic gum. Also, it was found that an increase in viscosity occurred at longer hydration time. More rheological and toxicological studies are required in order to analyze its possible application in food industries. (C) 2004 Wiley Periodicals, Inc.