Brain metastases arlsmg from lung tumours are relatively common. Metastasis formation involves events initiated by the tumour cell, including the release of proteolytic enzymes, cytokines and growth factors, and also the induction of angiogenesis Le. the formation of new blood vessels. Tumour cells migrate through the endothelial cell layer lining cerebral blood vessels and contact astrocytes (the main supporting cells of the brain). Characteristically a boundary forms around the metastasis restricting further brain invasion. The cellular processes involved in metastasis formation are largely unknown.Using an in vitro model this study investigated the cellular changes induced (', by human lung tumour cells on human astrocytes and endothelial cells. {\strocytic changes during direct cell:cell contact with lung tumour cells were examined as a model of boundary formation and a novel in vitro tubule formation assay was developed to examine the angiogenic potential of human lung tumour cells.