Korean scientists investigated whether St John’s wort (SJW) possesses a protective effect against hydrogen peroxide (H₂O₂)-induced cytotoxicity in neuronal cells. They performed 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetra-zolium bromide assay, 4,6-diamidino-2-phenylindole staining, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling assay, flow cytometry analysis, DNA fragmentation assay, and caspase-3 enzyme assay on SK-N-MC human neuroblastoma cells. Cells treated with (H₂O₂) exhibited several apoptotic features, while those pretreated with SJW prior to exposure showed a decreased occurrence of apoptotic features. In addition, pretreatment with SJW inhibited (H₂O₂)-induced increase in caspase-3 enzyme activity. St John’s wort may exert a protective effect against H₂O₂-induced apoptosis in human neuroblastoma cells.