Degradation of extracellular matrix, is a prerequisite for processes like tumor invasion and angiogenesis. Numerous studies indicate that plasminogen activation, initiated by u-PA, is a key process in malignant tumor growth. The expression of u-PA as well as its receptor is increased in malignant ovarian tumors. Additionally, u-PA stimulates signal transduction leading to cell proliferation and migration in certain cells. Material and methods. Tissue samples from 24 ovarian tumors were formalin fixed and/or frozen. Immunohistochemistry (ICC) used monoclonal antibodies either to u-PA (American Diagnostica # 394, and our own 8E7), to human macrophage CD68 antigen, or to Aspergillus niger antigen for control. This was followed by preformed ABC-complex. In situ hybridisation (ISH) was performed on cryostate sections using a 1.3 kb "S-labelled cRNA-antisenseprobe, and the corresponding sense probe was used for control. Results. The ISH signal was positive in epithelium of benign, borderline and well differentiated tumors. ICC staining was also positive in the epithelium and in occasional stromal cells. In intermediately differentiated tumors the ISH signal and ICC staining varied between epithelium and stroma in different areas. Poorly differentiated tumors had very strong signal in the stroma, but weak or absent signal in the epithelium. Conclusions. u-PA was almost exclusively expressed in the stroma of poorly differentiated tumors. Stromal u-PA may partly be related to the macrophages, but is also likely to be produced by regular stromal cells. u-PA produced by the stromal cells may bind to receptors either on these cells or other cells, i.e. cancer cells and capillary endothelial cells, which would imply a potential paracrine stimulation of proteolysis, migration or proliferation in these cells.