The preparation and characterization of a carbon paste electrode modified with poly(dopamine) as well as its novel application for the electrochemical oxidation and voltammetric determination of ranitidine are described. The sensitivity of the voltammetric measurements was significantly increased at modified electrode in comparison to the bare one. Besides, a further increase in the detecting sensitivity of ranitidine could be obtained in the presence of anionic surfactant (sodium dodecylsulfate). Using square-wave voltammetry, the drug yielded a well-defined voltammetric response in Britton-Robinson buffer (pH 5.0) containing 1 x 10(-3) M sodium dodecylsulfate at + 0.96 V (vs. Ag/AgCl). The process could be used to determine ranitidine in the concentration range from 1 x 10(-7) to 7.5 x 10(-6) M, with a detection limit of 1.9 x 10(-8) M (6.1 ng mL(-1)). The suggested method was successfully applied to pharmaceuticals and spiked human urine samples.