We have previously described an automated system (ECIS/taxis) for measuring chemotactic movement of Dictyostelium amoebae in a folic acid gradient [Hadjout, N., Laevsky, G., Knecht, D.A. and Lynes, M.A., 2001. Automated real-time measurement of chemotactic cell motility. Biotechniques 31, 1130-1138.]. In the ECIS/taxis system, cells migrate in an under-agarose environment, and their position is monitored by determining the impedance change caused by cells crawling onto the surface of an electrode. In this report, we show that chemotaxis of primary and immortalized leukocytes in response to complement (C5a) could be measured using the ECIS/taxis system. Several modifications to the design of the target electrode were tested, and a linear electrode perpendicular to the direction of movement was found to increase the sensitivity and reliability of the assay. Using the optimized ECIS/taxis assay, the dose response of neutrophils and WBC 265-9C cells was established and compared to the Boyden chamber assay. The ECIS/taxis assay system can be used to compare the movement of different cell types, to assess the effect of complex chemotactic gradients, or to determine the effects of pharmaceuticals on chemotactic motility.