Despite the fact that bacterial solute transport has been intensively studied for the last two decades, it has not yet been possible to describe the molecular mechanism of any transport process, largely due to the difficulties involved in handling membrane proteins and the lack of convenient in vitro assay procedures. The phosphoenolpyruvate: glycose phosphotransferase, a multiprotein system consisting of both soluble and membrane-bound components and with an associated chemical reaction which can be measured in cell-free extracts, has considerable potential for attaining this goal. Although the PTS is extremely complex, our understanding of the mechanisms by which it mediates and regulates carbohydrate transport in enteric bacteria is at an advanced stage.