The development of procedures for the reconstitution of protein translocation in the endoplasmic reticulum (ER) has allowed substantial new insights into the molecular mechanism of translocation. With these techniques, investigators are beginning to address the functional role of individual membrane and lumenal protein components in translocation. Efforts are now focused on the functional analysis of the translocation channel, the regulation of ribosome binding and the role of molecular chaperones in vectorial transport across the lipid bilayer. Current models of translocation suggest a system of remarkable simplicity; the molecular mechanism of translocation, however, remains elusive. ©1996 Academic Press Ltd.