Matrix metalloproteinases (MMPs) are a growing family of zinc-dependent endopeptidases which are characterised by their ability to degrade various extracellular matrix (ECM) components. The family includes collagenases, gelatinases, stromelysins, metalloelastase and membrane type metalloproteinases. Consistent with their proteolytic activities, MMPs have been implicated in a variety of physiological and pathological conditions, such as normal embryogenesis, tissue morphogenesis and are thought to play a role in facilitating tumour cell invasion of the normal brain. In this comparative study, we have used zymography, immunohistochemical and immunocytochemical techniques to demonstrate the expression of gelatinase-A and B (MMP-2 and 9, respectively) and membrane type metalloproteinase (MMP-14) in 8 intrinsic human primary brain tumours of various histological type and grade. Zymography results showed that MMP-2 was the most prominent proteolytic enzyme in all the cell lines studied (with one exception), while MMP-9 was only faintly expressed. However, the corresponding paraffin sections showed no expression of either MMP-2, 9 or 14 within the tumour cells, positivity being confined to haematogenous cells and the vascular endothelium. Fluorescence immunocytochemical studies, using monoclonal antibodies to MMP-2, 9 and 14, showed granular cytoplasmic reactivity in vitro. In addition, there was strong focal positivity at the cell membrane with MMP-14 in some high grade tumours suggesting that MMPs are produced at the leading edge of the cell by individual subpopulations of invading glia, in small quantities and on demand in vivo. It can be concluded that local microenvironmental conditions in vitro appear to stimulate such MMP activity.