Cellular migration is an essential component of invasive biological processes, many of which have been correlated with an increase in plasminogen activator production. Endothelial cell migration occurs in vivo during repair of vascular lesions and angiogenesis, and can be induced in vitro by wounding a confluent monolayer of cells. By combining the wounded monolayer model with a substrate overlay technique, we show that cells migrating from the edges of an experimental wound display an increase in urokinase-type plasminogen activator (uPA) activity, and that this activity reverts to background levels upon cessation of movement, when the wound has closed. Our results demonstrate a direct temporal relationship between endothelial cell migration and uPA activity, and suggest that induction of uPA activity is a component of the migratory process.