BACKGROUND: Parkinson disease (PD) is caused by selective cell death of dopaminergic neurons in the substantia nigra. An early onset form of PD, autosomal recessive juvenile parkinsonism has been associated with a mutation in the parkin gene. The function of parkin is known to remove misfolding proteins and protect cell death. We aimed to investigate the role of parkin against oxidative stress in neuronal cells. METHODS: Parkin knockout embryonic stem cells (PKO ES cells) were differentiated into neurons by adherent monolayer culture method. Oxidative stress was induced by the treatment of 1-methyl-4-phenylpyridinium (MPP+) in neurons derived from wild type and PKO ES cells, and cell viability was examined by MTT assay. After exposure to MPP+, Tuj1-positive cell population was compared between PKO and wild type cells by fluorescence activated cell sorter (FACS) analysis. The activated caspase3 protein level was also measured by Western blot analysis, FACS and immunocytochemistry. RESULTS: There was no difference in the efficiency of neuronal differentiation between wild type and PKO ES cells. After exposure to MPP+, no significant differences were found in cell viability and Tuj1-positive cell population between the two groups determined by MTT assay and FACS analysis, respectively. The activated caspase3 protein levels examined by Western blot analysis, FACS and immunocytochemistry were not changed in PKO cells compared with those of wild type cells after MPP+ treatment. CONCLUSION: These results suggest that PKO neuronal cells including dopaminergic neurons are not sensitive to caspase3-dependent cell death pathway during the response against MPP+-induced oxidative stress.