A method for preparing intact peribacteroid units from soybean nodules is described in detail. The polypeptide compositions of the peribacteroid membrane and peribacteroid space contents are described, and the properties of these compartments are discussed In the hght of recent literature. Evidence is presented that the peribacteroid membrane is permeable to succinate and malate but not to sucrose and glutamate. A dicarboxylate transporter on the peribacteroid membrane, which is capable of transporting malate and succinate at rates sufficient to support measured nitrogenase activity, is described The properties of an ATPase found on the peribacteroid membrane are also described and compared to those described in other reports This ATPase is able to catalyse energisation of the peribacteroid membrane in an uncoupler and vanadate-sensitive manner and may play an important role in the regulation of ion movements across the membrane.