The goal of this study was to determine whether the extracellular regulated kinases (ERK1/2) are involved in leukocyte transmigration across airway epithelium and the associated changes in epithelial permeability. In vitro, we used formyl-methionyl-leucyl-phenylalanine (fMLP) to induce migration of HL-60 cells (a human leukocyte cell line) across sheets of polarized Calu-3 airway epithelial cells and also to induce migration of human neutrophils across primary cultures of cow tracheal epithelial cells. In both systems, leukocyte migration decreased transepithelial electrical resistance (R(te)), increased epithelial permeability to albumin (P(alb)), and increased ERK1/2 phosphorylation in epithelial cells. Leukocyte migration and the associated changes in R(te), P(alb), and ERK1/2 phosphorylation were inhibited by calphostin C, a blocker of protein kinase C (PKC), and by PD98059 (a blocker of ERK1/2). Leukocyte transmigration in rat tracheas in vivo was induced with fMLP, and was associated with increased P(alb) and phosphorylation of epithelial ERK1/2. Again, migration and the associated changes were inhibited by luminal PD98059 or calphostin C though neither agent affected rat leukocyte migration in Boyden chambers in vitro. We conclude that PKC and ERK1/2 pathways are activated in airway epithelial cells during migration of leukocytes and are important regulators of airway epithelial permeability.