It was found that an exo-biopolymer (M.W. 1,000,000, molar ratio of 1.5:1.7:1.2:0.6:0.9, glucose:galactose:xylose:mannose:fructose, purity 99%) purified from the liquid culture broth of Hericium erinaceus mycelium enhanced the growth of rat adrenal nerve cells. The polymer also improved the extension of the neurites of PC12 cell. Its efficacy was found to be higher than those from known nerve growth factors such as Nerve Growth Factor (NGF) and Brain-Derived Nerve Factor (BDNF). The effect of two standards has not been observed above 0.1 (mg l(-1)) of supplementation; however, the polymer did show the effect of cell growth and neurite extension at up to 1.0 (mg l(-1)) of addition. While the polymer improved both cell growth and neurite extension, NGF and BDNF did only outgrowth of the neurites. Maximum cell density and length of the neurites were observed as 1.5x10(5) (viable cells ml(-1)) and 230 mum, respectively in adding 0.8 (mg l(-1)) of the biopolymer for 8 days cultivation. The control growth was observed only as 1.2x10(5) (viable cell ml(-1)) of maximum cell density and 140 mum of maximum length, respectively. It was also confirmed that the polymer reacted with the nerve cells within 30 min after adding the sample, compared to 80 min in adding two other growth factors. Number of neurite-bearing cells remained relatively steady in adding the polymer even when the cell growth started to be decreased. It was interesting that the polymer effectively delayed apoptosis of PC12 cells by dramatically reducing the ratio of apoptotic cells to 20% from 50% of the control.