The electrochemical behaviors of bismuth at random array carbon fiber microelectrodes (RACFMEs) are studied by cyclic voltammetry. Obtained results indicate that dissolution of bismuth is facilitated in the presence of cysteine, by formation of bismuth cysteinate on electrode surface. Ex situ prepared bismuth film random array carbon fiber microelectrodes (BiF-RACFMEs) were applied for determination of cysteine and N-acetyl cysteine (NAC) by using square wave cathodic stripping voltammetry (SWCSV). Formation of bismuth cysteinate was performed at -0.4 V. followed by bismuth reduction during cathodic sweep. The electrodes presented a linear response range toward cysteine and NAC, with estimated detection limits of 0.028 mu mol L-1 and 0.069 mu mol L-1, respectively. In the case of NAC two different linear concentration ranges of 0.1 mu mol L-1 to 1.0 mu mol L-1 and of 1.0 mu mol L-1 to 10.0 mu mol L-1 were obtained. The prepared BiF-RACFMEs have been successfully applied for determination of NAC in pharmaceutical samples (food supplement) with excellent recoveries. (C) 2013 Elsevier B.V. All rights reserved.