An isopropyl xanthate ion-selective electrode was constructed using as a carrier the complex trioctylmethylammonium-isopropyl xanthate. Two kinds of plastic membranes were built, with dioctyl phthalate (DOA) and dioctyl adipate as plasticizers. In both cases, the electrical responses were linear in a wide range of xanthate concentrations, with the limit of detection between 10(-4) and 10(-5) M. The electrical response was improved by adding only 3 mu mol of dodecyl alcohol per membrane. This fact seems to indicate not only that the fluidity is relevant but also that the surface polarity of the plastic membrane plays an important role. The analysis of some added salts shows that isobutyl xanthate is a strong interfering agent for the DOA electrode. Nitrate interferes weakly, whereas chloride, acetate, and carbonate do not affect the electrical response of both kinds of electrodes.