Construction and characterization of potentiometric membrane sensors for quantification of diclofenac and warfarin drugs are described. The membranes of the sensors incorporate 1.8 wt.% iron(II)-phthalocyanine (Pc) as a molecular recognition reagent, 64.3 wt.% dibutylsebacate (DBS) solvent mediator, 1.8 wt.% tridodecylmethylammonium chloride (TDMAC) as membrane additive and 32.1 wt.% poly(vinyl chloride) (PVC) as a matrix. The sensors display linear response for 1 x 10(-2) to 9 x 10(-6) mol l(-1) (detection limit 5.4 x 10(-6) mol l(-1)) and 1 x 10(-2) to 5 x 10(-6) mol l(-1) (detection limit 3 x 10(-6) mol l(-1)) with anionic slopes of -61 +/- 1 and -63 +/- 1 mVdecade(-1) over the pH range 5.5-9 for declofenac and warfarin, respectively. Validation of the assay methods according to the quality assurance standards confirms their suitability for quality control purposes. Use of the sensor for the assay of various formulations of the drugs shows a mean average recovery of 99.7% of the nominal values and a mean precision of +/-0.3%. Significantly improved accuracy, precision, response time, stability, selectivity and sensitivity are offered by these simple and cost-effective potentiometric sensors compared with other standard techniques. LESS