Although neuronal cells are highly vulnerable to oxidative stress, recent studies suggest that production of reactive oxygen species (ROS) increases during and is essential for neuronal differentiation. In addition, we have previously found that heme biosynthesis is up-regulated during retinoic acid-induced differentiation of Neuro2a cells. In the current study, we showed that this up-regulation of heme biosynthesis during differentiation is ROS-dependent. Furthermore, we found that ROS-dependent induction of heme oxygenase, which degrades heme and acts as an anti-oxidant, and catalase, another anti-oxidant enzyme that contains heme as a prosthetic group, occurs during differentiation. These results suggest that heme biosynthesis following the degradation of heme protects Neuro2a cells from oxidative stress caused by ROS during differentiation. (c) 2007 Elsevier Inc. All rights reserved.