We have developed a computer-based image analysis system to measure in-filter migration of human neutrophils in the Boyden chamber. This method is compared with the conventional manual counting techniques. Neutrophils from healthy individuals and from patients with reduced chemotactic activity were used. The cells migrating into the filter were counted automatically at depths 20 microns apart commencing from the upper surface on the filter. The major advantages of this method are reproducibility and the counting of many fields which provides better data for statistical analysis of the results. Another advantage of the assay is that it can be used to show the migration pattern of different populations of neutrophils from both healthy individuals and patients.