Abstract The quantitation of chemotaxis in vitro was developed with a computer-assisted scanning densitometer. The method of estimating the number of cells on a filter was based on the photo-reflection from the nuclei of stained cells. Samples obtained from a 48-well micro chemotaxis assembly were successfully analyzed by this method. This assay system could quantitate chemotaxis much faster and more accurately than by cell counting under the microscope. It was sensitive enough to determine the responsiveness of SMCs and fibroblasts to various chemoattractants. This system could be applied to medical and biological screening tests for drugs and clones in laboratories.