An anti-fibronectin receptor monoclonal antibody preferentially labels the leading edges of freshly plated CHO fibroblasts, suggesting that this receptor circulates through the endocytic cycle. Using a new labelling reagent, I show that this receptor is indeed endocytosed at 37 degrees C and then returned to the cell surface. These findings imply that fibronectin receptors are recirculated to the leading edge of a motile cell by the endocytic cycle, and establish that the processes of endocytosis/exocytosis and cell locomotion are intimately linked.