The method described here for the quantitation of cell migration in Boyden chambers is applicable to many cell types, especially connective tissue cells and endothelial cells. Currently, there are many groups working toward the isolation of chemotactic factors for these cells and this method would be useful for the large numbers of repetitive assays done during a purification. In our hands the assay is very reproducible and can be learned within a short time. The major problem with the assay is that the upper surface cells must be completely removed as well as any cellular debris containing dye. However, if the proper care is used in removing these cells, the results vary less than those obtained by counting cells directly.