The metabolic microenvironment of tumors differs profoundly from normal tissues and affects both malignant potential and efficacy of tumor treatments. A commonly found characteristic is acidosis reflecting the glycolytic metabolism. The aim of the present work was to study the impact of extracellular acidosis on cell signaling. Additionally, pH-dependent changes of cell survival, metabolism as well as tumor cell motility and invasiveness were analyzed. Acidosis led to an activation of the MAP kinases ERK1/2 and p38 which depended on reactive oxygen species. Furthermore, tumor cell migration was increased, but independently of ERK1/2 and p38. From these results on the impact of acidosis on cellular signaling and cell motility new approaches for an individualized tumor treatment can be developed.