The pathogenesis of Parkinson's disease (PD) is not completely understood, Zinc (Zn2+) and dopamine (DA) have been shown to involve in the degeneration of dopaminergic cells. By microarray analysis, we identified Gadd45b as a candidate molecule that mediates Zn2+ and DA-induced cell death; the mRNA and protein levels of Gadd45b are increased by Zn2+ treatment and raised to an even higher level by Zn2+ plus DA treatment. Zn2+ plus DA treatment-induced PC12 cell death was enhanced when there was over-expression of Gadd45b and was decreased by knock down of Gadd45b. MAPK p38 and JNK signaling was able to cross-talk with Gadd45b during Zn2+ and DA treatment. The synergistic effects of Zn2+ and DA on PC12 cell death can be accounted for by an activation of the Gadd45b-induced cell death pathway and an inhibition of p38/JNK survival pathway. Furthermore, the in vivo results show that the levels of Gadd45b protein expression and phosphorylation of p38 were increased in the substantia nigra by the infusion of Zn2+/DA in the mouse brain and the level of Gadd45b mRNA is significantly higher in the substantia nigra of male PD patients than normal controls. The novel role of Gadd45b and its interactions with JNK and p38 will help our understanding of the pathogenesis of PD and help the development of future treatments for PD. (Figure presented.) Zinc and dopamine are implicated in the degeneration of dopaminergic neurons. We previously demonstrated that zinc and dopamine induced synergistic effects on PC12 cell death. Results from this study show that these synergistic effects can be accounted for by activation of the Gadd45b-induced cell death pathway and inhibition of the p38/JNK survival pathway. We provide in vitro and in vivo evidence to support a novel role for Gadd45b in the pathogenesis of Parkinson's disease.