Through its type 1 receptor (TNFR1), the cytokine TNF elicits an unusually wide range of biological responses, including inflammation, tumor necrosis, cell proliferation, differentiation, and apoptosis. We investigated how TNFR1 activates different effector functions; the protein kinase JNK, transcription factor NF-κB, and apoptosis. We found that the three responses are mediated through separate pathways. Recruitment of the signal transducer FADD to the TNFR1 complex mediates apoptosis but not NF-κB or JNK activation. Two other signal transducers, RIP and TRAF2, mediate both JNK and NF-κB activation. These two responses, however, diverge downstream to TRAF2. Most importantly, JNK activation is not involved in induction of apoptosis, while activation of NF-κB protects against TNF-induced apoptosis.