The skin and liver may be targets for cytotoxicity induced by oxidative drug metabolites. We used human epidermoid A431 cells and human hepatoblastoma Hep G2 cells as the experimental model. The aim of the study was to investigate and evaluate the effect of silymarin on acetaminophen (APAP)-induced toxicity under controlled conditions. Silymarin is known to be a potent antioxidant that diminishes toxicity induced by a variety of other hepatotoxins (e.g. Amanita phaloides, algae’s toxins, carbon tetrachloride). Glutathione (GSH) depletion was enhanced by adding to the medium buthionine sulfoximine [L-buthionine- (SR)-sulfoximine, BSO]. Cells were incubated with high-concentration 5-20 mM APAP or Α-(minimum essential medium for 2-24 h to evaluate the drug’s ability to reduce cytoviability. Viability was then quantitated by metabolism of the tetrazolium dyes (MTT) and neutral red (NR). Cytoviability was 100% for controls. For Hep G2 treated for 24 h with 20 mM, APAP viability was 56.0% by MTT and 62.5% by NR. BSO-treated cells showed an enhanced cytotoxicity, determined by both assays. Administration of 0.5 mM silymarin reduced cytotoxicity significantly. In A431 cells, treatment with 20 mM APAP reduced viability by 57% (MTT) and 69% (NR) versus control (100%). BSO further decreased viability. Since incubation with silymarin showed significant protection against APAP toxicity, it can be considered a cytoprotective agent in this in vitro model of drug toxicity. GSH concentrations in both cell lines decrease significantly after exposure to 20 mM APAP, or 0.5 mM versus control (p < 0.05), and increased (p < 0.001) if incubated with APAP and silymarin. The protective effect could be through mitochondrial membrane stabilization and/or an increase in available GSH.