To determine whether recombinant NT-3 protein was biologically active, we studied their effects on the neurite outgrowth in human neuroblastoma cells. Primary human neuroblastoma cells were collected and cultured routinely. The attached cells were trypsinized by 0.05% trypsin (Invitrogen) for 10 min, and then the reaction was stopped by adding DMEM (Sigma) and Ham’s F-12 (1:1; Sigma) supplemented with 10% fetal bovine serum (DF-10S; Invitrogen). The suspension was washed twice in serum-free medium and seeded onto 4 plates at a density of 1×104. Then 500 μL medium from the cultures of OEGs transfected with pcDNA3.1(+)-NT3 or pcDNA3.1(+), or OEGs without plasmid transfection, was added to 3 different plates. The rest plate was added with serum-free medium. Three days later, neurite outgrowth was photographed.