Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide with potent neurotrophic and neuroprotective effects. We have previously shown that PACAP protects against several types of retinal injuries in vivo, including retinal ischemia, glutamate-induced excitotoxicity, UV A-induced lesion, and diabetic retinopathy. We have also shown that PACAP activates antiapoptotic pathways and inhibits proapoptotic signaling in retinal lesions in vivo. PACAP receptors have been identified on the retinal pigment epithelial cells and PACAP has been shown to inhibit interleukin secretion from pigment epithelial cells. It is not known, however, whether PACAP is protective in these cells. Human retinal pigment epithelial cells (ARPE-19 cell line) were exposed to in vitro oxidative stress by hydrogen peroxide. Cell survival was decreased in cells exposed to oxidative stress, which could be significantly and dose-dependently attenuated by 10 pM-1 μM PACAP treatment, as shown by MTT viability test. The protective effect of PACAP could be blocked by the receptor antagonist PACAP6-38. In addition, flow cytometry and JC-1 assay revealed that oxidative stress-induced apoptosis in retinal pigment epithelial cells could be decreased by PACAP treatment. In summary, these results show, for the first time, that PACAP is antiapoptotic in the retinal pigment epithelial cells.