Known inducers of the hepatic glutathione (GSH) S-transferases were tested at the limits of their solubility as inducers of the enzyme in cultured human keratinocytes. Neither phenobarbital, trans-stilbene oxide, propylthiouracil, nor butylated hydroxyanisole increased GSH S-transferase activity or led to the appearance of α- or μ-forms of the enzyme, as judged by Western blotting. Only the π-form of the enzyme was found before and after all treatments. Thus, the enzyme is not indu-cible in keratinocytes. However, 4 mM propylthiouracil did lead to a 50% increase in GSH reductase activity, and phenobarbital at 4 mM completely abolished GSH peroxidase and GSH reductase activity and led to a significant loss of viabili