Binding of tumor necrosis factor-alpha (TNFalpha) to its receptor, TNF-R1, results in the activation of inhibitor of kappaB kinase (IKK) and c-Jun N-terminal kinase (JNK) pathways that are coordinately regulated and important in survival and death. We demonstrated previously that in response to hydrogen peroxide (H2O2), the ability of TNFalpha to activate IKK in mouse lung epithelial cells (C10) was inhibited and that H2O2 alone was sufficient to activate JNK and induce cell death. In the current study, we investigated the involvement of TNF-R1 in H2O2-induced JNK activation. In lung fibroblasts from TNF-R1-deficient mice the ability of H2O2 to activate JNK was inhibited compared with fibroblasts from control mice. Additionally, in C10 cells expressing a mutant form of TNF-R1, H2O2-induced JNK activation was also inhibited. Immunoprecipitation of TNF-R1 revealed that in response to H2O2, the adapter proteins, TRADD and TRAF2, and JNK were recruited to the receptor. However, expression of the adaptor protein RIP, which is essential for IKK activation by TNFalpha, was decreased in cells exposed to H2O2, and its chaperone Hsp90 was cleaved. Furthermore, data demonstrating that expression of TRAF2 was not affected by H2O2 and that overexpression of TRAF2 was sufficient to activate JNK provide an explanation for the inability of H2O2 to activate IKK and for the selective activation of JNK by H2O2. Our data demonstrate that oxidative stress interferes with IKK activation while promoting JNK signaling, creating a signaling imbalance that may favor apoptosis.