The high migration rate of tumor cells often results in poor prognosis for the survival of the patients. Here, we describe a protocol to measure the migration of cells using a quantitative assay. The relative tumor cell migration was measured using ThinCertsTM cell culture inserts and a lactate dehydrogenase (LDH) assay to quantify the relative cell number. The quantification of the migration with the LDH kit is much more precise than other methods using i.e. crystal blue to count the cells.