Oxidative modifications of proteins are fundamental biochemical events that regulate cellular signaling, protein expression, and function. The redox status is balanced by reductants in which GSH plays a major role. This study investigated whether or not p21Waf1 expression and TNFalpha biosynthesis in macrophage differentiation/activation were regulated by GSH modulators and whether or not the JNK and ERK pathway were involved. We observed an increase of p21Waf1 expression and TNFalpha biosynthesis in the THP1 monocyte/macrophage cell line treated with PMA. Treatment of THP1 cultures with NAC prior to adding PMA abrogates the expression of p21Waf1 mRNA and decreases the level of TNFalpha whereas GSH depletion by BSO enhances the levels of TNFalpha with minor effects on p21Waf1 expression. To assess whether or not ERK and JNK were involved in the redox mechanism of p21Waf1 and TNFalpha, we used pharmacological inhibitors for JNK and ERK. Both PD98095 and dicoumarol were capable of blocking TNFalpha production but had only a small effect on p21Waf1 expression. We next observed that activation of JNK was significantly inhibited in cells pretreated with NAC with no effect on ERK. Taken together, our findings suggest that the modulation of GSH regulate the magnitude the cell response to PMA in which JNK and ERK have a particular role in redox signaling.