Streptococcus mutans ATCC-27607 produces exopolysaccharides that adhere to glass. In the normal geomagnetic field about 50% more polysaccharide adhere preferentially to glass surfaces facing North as compared to South facing surfaces. Reversal of the direction of the magnetic field by 180 degrees produces a similar reversal in the direction of the preferential accumulation. Reduction of the field by 90% abolishes the preferential accumulation.