Objective : The effects on neural proliferation and differentiation of neural stem cells (NSC) of basic fibroblast growth factor-2 (bFGF). insulin growth factor-I (IGF-I). brain-derived neurotrophic factor (BDNF). and nerve growth factor (NGF) were assessed. Also, following combinations of various factors were investigated : bFGF+IGF-I, bFGF+BDNF, bFGF+NGF, IGF-I+BDNF, IGF-I+NGF, and BDNF+NGF. Methods : Isolated NSC of Fisher 344 rats were cultured with individual growth factors, combinations of factors, and no growth factor (control) for 14 days. A proportion of neurons was analyzed using $eta$-tubulin III and NeuN as neural markers. Results : Neural differentiations in the presence of individual growth factors for $eta$-tubulin III-positive cells were : BDNF, 35.3%; IGF-I, 30.9%; bFGF, 18.1%; and NGF, 15.1%, and for NeuN-positive cells was : BDNF, 34.3%; bFGF, 32.2%; IGF-I, 26.6%; and NGF, 24.9%. However, neural differentiations in the absence of growth factor was only 2.6% for $eta$-tubulin III and 3.1% for NeuN. For $eta$-tubulin III-positive cells, neural differentiations were evident for the growth factor combinations as follows : bFGF+IGF-I, 73.1 %; bFGF+NGF, 65.4%; bFGF+BDNF, 58.7%; BDNF+IGF-I, 52.2%; NGF+IGF-I, 40.6%; and BDNF+NGF, 40.0%. For NeuN-positive cells : bFGF+IGF-I, 81.9%; bFGF+NGF, 63.5%; bFGF+BDNF, 62.8%; NGF+IGF-I, 62.3%; BDNF+NGF, 56.3%; and BDNF+IGF-I, 46.0%. Significant differences in neural differentiation were evident for single growth factor and combination of growth factors respectively (p<0.05). Conclusion : Combinations of growth factors have an additive effect on neural differentiation. The most prominent neural differentiation results from growth factor combinations involving bFGF and IGF-I. These findings suggest that the combination of a mitogenic action of bFGF and post-mitotic differentiation action of IGF-I synergistically affects neural proliferation and NSC differentiation.