Angiopoietin-1 (Ang-1) belongs to a novel family of endothelial growth factors that function as ligands for an endothelialspecific receptor tyrosine kinase (Tie-2). The Ang-/Tie-2 system may contribute to angiogenesis and vascular remodeling by mediating interactions of endothelial cells with smooth muscle cells and pericytes. The spatial distribution and temporal expression of Ang-1 and Tie-2 in the rat brain were studied following collagenase-induced intracerebral hemorrhage (ICH) by immunohistochemistry and reverse transcription-polymerase chain (RT-PCR) analysis, respectively. Immunohistochemical analysis revealed that some Ang-1 or Tie-2-positive dilated vessels resided around the hematoma and extended into the clot. RT-PCR analysis showed that Ang-1 and Tie-2 mRNA signal was detected at 2 days and persisted for 28 days after ICH. These findings suggest that ICH could lead to upregulation of Ang-1 and the receptor Tie-2 mRNA.