The human immunodeficiency virus (HIV) has been reported to target noninfected CD4 and CD8 cells for destruction. This effect is manifested in part through up-regulation of the death receptor Fas ligand (FasL) by HIV-1 negative factor (Nef), leading to bystander damage. However, the signal transduction and transcriptional regulation of this process remains elusive. Here, we provide evidence that p38 mitogen-activated protein kinase (MAPK) is required for this process. Loss-of-function experiments through dominant-negative p38 isoform, p38 siRNA, and chemical inhibitors of p38 activation suggest that p38 is necessary for Nef-induced activator protein-1 (AP-1) activation, as inhibition leads to an attenuation of AP-1-dependent transcription. Furthermore, mutagenesis of the FasL promoter reveals that its AP-1 enhancer element is required for Nef-mediated transcriptional activation. Therefore, a linear pathway for Nef-induced FasL expression that encompasses p38 and AP-1 has been elucidated. Furthermore, chemical inhibition of the p38 pathway attenuates HIV-1-mediated bystander killing of CD8 cells in vitro.