AbstractBasement membrane is a thin extracellular matrix that underlies epithelia and endothelia and separates them from the stroma. Tumor cells must cross this membrane to invade stroma and establish distant metastases. They do this by producing proteases that degrade the matrix. Of several in vitro models, those using Matrigel are the most reliable, reproducible, and representative of in vivo invasion. In the assay presented here, tumor cells are placed in the upper chamber of Boyden migration chamber. The upper and lower chambers are separated by a porous membrane coated with Matrigel. A chemoattractant in the lower well stimulates migration. After an interval, tumor cells are recovered from or counted on the lower surface of the membrane.