A carbon paste electrode modified with cobalt nanoparticles (CoNPs) was prepared and used for low level chlorpromazine (CPZ) determination in biological samples. The measurement was made using differential pulse voltammetry. The influence of some experimental variables such as carbon paste composition, working solution pH, supporting electrolyte, scan rate, pulse amplitude and possible interferences were studied. The modified carbon paste electrode exhibited a linear current response over the concentration range between 0.002 and 1.0 mu M CPZ, with a detection limit of 0.6 nM. The proposed sensor exhibited a high sensitivity, good selectivity and was successfully applied for clinical evaluation of CPZ. (c) 2012 Elsevier B.V. All rights reserved.