A highly selective potentiometric sensor for thiocyanate ion based on the use of a newly synthesized organo-palladium ion exchanger complex dispersed in a plasticized poly(vinyl chloride) membrane is described. The sensor displays a Nernstian response (À 57.8 AE 0.2 mV decade À1 ) over a wide linear concentration range of thiocyanate (1.0 Â 10 À6 -1.0 Â 10 À1 mol L À1 ), low detection limit (6.3 Â 10 À7 mol L À1 ), fast response (20 s), stable potential readings (AE 0.4 mV), good reproducibility (AE 0.9%), long term stability (8 weeks), high precision (AE 0.7%) and applicability over a wide pH range (4 -10). Negligible interferences are caused by F À , Cl À , I À , Br À , NO 3 À , NO 2 À , CN À , SO 4 2À , S 2 O 3 2À , PO 4 3À , citrate, acetate and oxalate ions. Under hydrodynamic mode of operation (FIA), the calibration slope is À 51.1 AE 0.1 mV decade À1 , the linear response range is 1.0 Â 10 À5 -1.0 Â 10 À1 mol L À1 SCN À and the sample throughput is 40 -45 per hour. The sensor is satisfactory used for manual and flow injection potentiometric determination of SCN À in the saliva and urine of cigarette smokers and non smokers. The data agree fairly well with results obtained by the standard spectrophotometric technique. Direct potentiometry and potentiometric titration of SCN À with Ag þ are also monitored with the sensor.