Metabolic acidosis (MA) is a severe disturbance of acid-base balance leading to the adaptive increase in renal acid excretion. This adaption requires the concerted regulation of metabolic and transport pathways which are only partially understood. Therefore we aim to characterize the transcriptional changes in the kidney during metabolic acidosis. To induce acidosis C57BL/6 mice were given NH4Cl in the drinking water for 2 or 7 days or were left untreated. To confirm MA, urine and blood was analyzed and showed the hallmarks of MA, i.e. lower blood pH and HCO3, urinary acidification and increased ammonia excretion. Western blot and real-time PCR experiments also confirmed higher expression of PEPCK and SNAT1 in the kidneys from NH4Cl treated mice, two genes known to be upregulated during MA. RNA form these kidneys is being hybridized using cDNA microarrays (Applied Biosystems) and analyzed for transcriptional changes.