The detection and quantification of uric acid (UA) and ascorbic acid (AA) in different biological fluids such as serum is very important in clinical diagnosis. In this study, a sonogel-carbon electrode modified with L-cysteine was used for detection and quantification of these molecules by cyclic voltammetry (CV) and square wave voltammetry (SWV). These two methods are known for their suitability for monitoring of bioactive molecules in biological samples. Optimization of parameters affecting selectivity and sensitivity of these two methods is included. The peak current showed a linear relationship with the concentrations of UA and AA in the range of 10(-5) M to 10(-4) M for UA and 5 x 10(-5) M respectively. The detection limit was of 10(-5) M for UA and 5 x 10(-5) M for AA. In addition, the interference of UA and AA was also studied. A neat separation of the oxidation peaks of these two compounds with a peak-to-peak separation of 295 mV was registered. The results indicate that carbon electrode modified with L-cysteine can successfully be used for a selective and sensitive simultaneous determination of UA and AA in the serum. (C) 2015 Elsevier B.V. All rights reserved.