The complex formed by two members of the S100 calcium-binding protein family, S100A8/A9, exerts apoptosis-inducing activity against various cells, especially tumor cells. Here, we present evidence that S100A8/A9 also has cell growth-promoting activity at low concentrations. Receptor of advanced glycation end product (RAGE) gene silencing and cotreatment with a RAGE-specific blocking antibody revealed that this activity was mediated via RAGE ligation. To investigate the signaling pathways, MAPK phosphorylation and NF-kappaB activation were characterized in S100A8/A9-treated cells. S100A8/A9 caused a significant increase in p38 MAPK and p44/42 kinase phosphorylation, and the status of stress-activated protein kinase/JNK phosphorylation remained unchanged. Treatment of cells with S100A8/A9 also enhanced NF-kappaB activation. RAGE small interfering RNA pretreatment abrogated the S100A8/A9-induced NF-kappaB activation. Our data indicate that S100A8/A9-promoted cell growth occurs through RAGE signaling and activation of NF-kappaB.