In the last eighteen months, it has become clear that some classes of proteins are actively recruited into endoplasmic reticulum export carriers, whereas others are exported as bulk-flow cargo. Subsequent transport to the Golgi is mediated by tubulovesicular membranes. The anterograde membrane flow is compensated for by a retrograde pathway, which, in addition to the recycling of membrane and proteins to the endoplasmic reticulum, may play a role in anterograde cargo concentration.