Purpose: To determine the role of matrix metalloproteinases (MMP) -1,-2 & -9 in directing the behaviour of human retinal pigment epithelial (HRPE) cells during contraction of 3-D collagen gels. Methods. The effect of HRPE cells on collagen gel invasion and contraction were quantified by using phase contrast microscopy. Immunohistochemistry of the gel using monoclonal antibodies against MMP-1, -2 & -9 was performed. The effects of MMP inhibitor, BB-94 on cultured HRPE cells and gel contraction were observed. Results. HRPE cells mostly proliferated as sheets of cells on the surface of the collagen gel and only minimally invaded the gel. However, some HRPE cells were seen to invade the gel as single cells detaching from the surface sheets. Surface-located sheets of cells exerted a dose- dependent contraction on the gel and generally failed to express MMPs. Single cells invading the gel expressed MMP-2 & -9. No expression of MMP-1 was observed by HRPE cells. BB-94, at a dose of 500nM and 5M, reduced the amount of gel contraction. Conclusions. These data indicate that MMPs are selectively involved in HRPE invasion and collagen gel contraction. Both these processes may be implicated in the pathogenesis of similar conditions in vivo in which contraction of collagen gel is a feature e.g. proliferative vitreoretinopathy (PVR).