An effective electrochemical sensor for the selective determination of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA) in 0.04 mol L-1 universal buffer solution (pH 7.4) is introduced. The sensor is based on a carbon paste (CP) electrode modified with gold nanoparticles. In a mixture of DA, AA, and UA, the sensor shows high selective response toward DA and no response for AA or UA. The effect of various experimental parameters including time of deposition of gold nanoparticles on the CP electrode, pH, and scan rate on the voltammetric response of DA was investigated. At the optimum conditions, the concentration of DA was determined using differential pulse voltammetry in a linear range of 1.0 x 10(-7) to 5.0 x 10(-6) mol L-1 and 5.0 x 10(-6) to 1.3 x 10(-4) mol L-1 with correlation coefficients of 0.9995 and 0.9988 and a detection limit of 5.9 x 10(-9) and 8.2 x 10(-8) mol L-1, respectively. The modified electrode can be used for the determination of DA spiked into human serum samples, and excellent recovery results were obtained over a wide concentration range of DA. Moreover, validation parameters, such as reproducibility, sensitivity, and recovery were evaluated successfully in the determination of DA in diluted human urine. (C) 2010 The Electrochemical Society. [DOI:10.1149/1.3456629] All rights reserved.