monocarboxylate transporter (MCT) are vital transmembrane transporters involved in multiple cellular functions including the regulation of intracellular pH and lactate transport. At least eight isoforms of MCT have been cloned and characterized to date, they constitute a new gene family of mammal transporters. These isoforms have the differences in substrate and inhibitor specificities and tissue distribution. Thus it may provide a new way of diagonosis and treating for dieases such as cancer by investigating on the structure and function and regulational mechanism of MCT.