This study provides evidence that expression of EphA8 receptor in NG108-15 cells results in a substantial increase in the number of neurite-bearing cells. However, the EphA8-induced neurite outgrowth does not require either ephrin-A5 stimulation or ectopic expression of $p110{gamma}$ PI-3 kinase. In contrast, co-expression of a lipid kinase-inactive $p110{gamma}$ mutant together with EphA8 causes neurite retraction in the presence of ephrin-A5 stimulation. This effect was not observed in the absence of ephrin-A5 stimulation. Significantly, the tyrosine kinase activity of EphA8 is not important for either of these processes. Taken together, our results strongly suggest that $p110{gamma}$ PI-3 kinase is critically involved in the regulatory process by which ephrin-A5 exerts effects on the EphA8-induced neurite outgrowth.