Different in vitro invasion assays have been established to assess tumour cell invasiveness. We compared the invasiveness of previously described cell lines from human breast cancer that are derived from cancers in an early or late stage of malignancy, by three different in vitro systems. First, we evaluated the capacity of the cells to go through a Matrigel barrier in a Boyden chamber, and in a second assay their ability to migrate in a thick layer of collagen. These experiments showed that early stage cells were more motile than late stage cells. By a third assay, we tested the ability of cells to invade chick heart fragment tissue and found none of the cells to be invasive.