Immunostimulatory polysaccharides can be preferentially extracted from
food-grade microalgae using an aqueous ethanol extraction procedure. The
resulting preparations exhibit extremely potent immunostimulatory
activity. The preferential extraction of these immunostimulatory
polysaccharides is dependent on the concentration of ethanol used and the
extraction temperature. The most efficient conditions are 50% ethanol
concentration at temperatures between 60.degree. and 70.degree. C. The
isolated polysaccharide preparations are potentially useful as a
botanical or pharmaceutical preparation to improve immune function.