To test the effects of a sulfated polysaccharide, Haishen (HS) on the viability and proliferation of neural stem/progenitor cells (NSPCs), we isolated the polysaccharide from the body wall of the sea cucumber Stichopus japonicus by enzymolysis extraction, anion-exchange and gel-permeation chromatography. HS is a highly sulfated fucoidan with a molecular weight of 4.23 x 10(5) Da. Due to its safety being of invertebrate origin they are less likely to contain infectious agents, the effects of HS on the viability and proliferation of NSPCs in vitro were examined by MTT assay, BrdU labeling and neurosphere formation assay, respectively. Our results showed that HS alone increased NSPC viability in a dose-dependent manner. Moreover, HS acted synergistically with fibroblast growth factor-2 (FGF-2) but not epidermal growth factor (EGF) to enhance the proliferation of NSPCs. Finally, HS did not induce apoptosis of NSPCs. Our findings suggest that HS can serve as an adjuvant for promoting the proliferation of NSPCs. (C) 2009, The Society for Biotechnology, Japan. All rights reserved.