 A combination of NGF, glial cell-line derived neurotrophic factor (GDNF), and ciliary neurotrophic factor (CNTF) was presented to Dorsal root ganglion cultures "in vitro".One factor from each neurotrophic family was used.It was determined that there is not a difference in individual optimal concentration and combinatorial optimal concentration; however, around day 5 or 6 the neurites ceased extension and began to degrade.