The effects of environmental parameters on polysaccharide formation by Ganoderma lucidum were investigated in submerged cultures. The optimal temperature and pH was 30-35 degrees C and 4-4.5, respectively, in a glucose-ammonium chloride medium and polysaccharide concentration reached 1.6 mg/ml. Agitation and aeration influenced the formation and secretion of polysaccharide. The optimal rotating speed was 150 rpm in 7-day flask cultures, while the agitation speed employed in fermenter culture greatly affected the production rate and maximum concentration of polysaccharide. Although higher speeds enhanced mixing efficiency and polysaccharide release, higher shear stress had a detrimental effect on mycelial growth and polysaccharide formation.