Vitronectin is expressed in a cell-specific manner in the developing brain and concentrated in the brain during disease processes, such as germinal matrix hemorrhage and infarction, in which there is breakdown of the blood-brain barrier. In this study, we identified the integrin receptors that mediate attachment of primary neonatal rat astrocytes to vitronectin. Using fluorescent activated cell sorter and immunoprecipitation analyses, we established that the vitronectin receptor integrins αvβ5 and α8β1, but not αvβ3, are expressed on neonatal rat astrocytes. Attachment of the neonatal astrocytes to vitronectin was inhibited (85%) in an additive manner by neutralizing anti-αvβ5 and anti-β1 antibodies. Attachment to vitronectin was also inhibited in a dose-dependent manner by the type I plasminogen activator inhibitor (PAI-1), a serine protease inhibitor. Our data demonstrate that unstimulated primary neonatal rat astrocytes attach to vitronectin, utilizing integrins αvβ5 and α8β1, and that this attachment is regulated by PAI-1. Copyright (C) 2000 Elsevier Science Ireland Ltd.