This paper describes a simple and convenient method to measure the concentration and time response function f (C,t) of cells exposed to a toxicant by electric cell-substrate impedance sensing. Attachment and spreading of fibroblastic V79 cells cultured on small gold electrodes precoated with fibronectin were detected as electrical resistance changes. With this method, chemical cytotoxicity was easily screened by observing the response function of attached cells in the presence of inhibitor. The cytotoxicities of three test models, cadmium chloride, sodium arsenate, and benzalkonium chloride, were quantified by measuring the percentage inhibition as a function of the inhibitor concentration. The half-inhibition concentration, the required concentration to achieve 50% inhibition, derived from the response function agreed well with the results obtained using the standard neutral red assay.