This paper describes the preparation and use of a tubular electrode by means of chemical pretreatment of a silver tube with mercuric (II) chloride solution and iodide solution in flow injection analysis (FIA). The electrode was used as a potentiometric sensor for the indirect determination of vitamin C and glutathione in a carrier stream containing iodine. A simple FIA system that consists of a peristaltic pump, an injection T valve, a tubular silver electrode and a saturated calomel reference electrode (SCE) was used. Some typical FIA parameters such as flow rate, tube length, sample volume and composition of the carrier stream were varied. After optimisation of these parameters, the electrode was further characterised by a constant linear response within the concentration range for the vitamin C between 5 x 10(-5) and 5 x 10(-3) M at the slope of 60.5 +/- 1.0 mV/p (vitamin C). Glutathione has a linear concentration range between 5 x 10(-5) and 10(-2) M at a slope of 55.2 +/- 1.0 mV/p (glutathione). The experimental slope was in good agreement with the theoretical values. Some pharmaceutical products containing vitamin C were also tested. These results can be compared to the results obtained by the standard volumetric method for the determination of vitamin C and are also in good agreement with values declared by pharmaceutical manufacturers.