Complement-mediated pulmonary edema results from increases in lung capillary hydraulic conductivity (Lp), possibly by receptor-mediated mechanisms. We considered the Lp effects of vitronectin and the vitronectin-containing complement complex SC5b-9, which ligate the integrin α_vβ₃. Vitronectin, SC5b-9, and SC5b-9–enriched zymosan-activated serum all rapidly increased Lp, as determined by the split-drop technique in single lung capillaries of rat lung. The Lp increases were inhibited by a monospecific (LM609) and a polyclonal (R838) antibody against the α_vβ₃ integrin but not by an irrelevant monoclonal antibody isotype matched with LM609, by a monoclonal antibody against the α_vβ₅ integrin, or by preimmune rabbit serum. Vitronectin monomers failed to increase Lp. The tyrosine kinase blockers genistein and methyl 2,5-dihydroxycinnamate caused significant concentration-dependent inhibitions of Lp increases due to vitronectin and zymosan-activated serum. By contrast, the protein kinase C blocker calphostin C had no major effect. We conclude that (1) multivalent ligation of the luminally located α_vβ₃ integrin of lung capillary endothelium increases transcapillary liquid flux, and (2) the dominant signal transduction pathway for this effect occurs through tyrosine kinase activation.