Abstract The ability of capillary zone electrophoresis in the development of analytical methods devoted to the quality control of the thiol drug penicillamine is shown. Using 50 m M phosphate running buffer (pH 2.5), good quantitations of underivatized penicillamine and its disulfide were achieved; detection at 200 nm allowed checking the presence of the disulfide impurity in pharmaceuticals. The use of 1,1′-[ethenylidenebis(sulfonyl)]bis-benzene as a thiol specific reagent resulted in an increased sensitivity for the quantitation of d-penicillamine (limit of detection at 200 nm wavelength was 1.5 μ M). Introducing β-cyclodextrin as chiral selector in the running buffer, enantioseparation of d, l-penicillamine was obtained; for this purpose (+)-camphor-10-sulfonic acid, a chiral ion-pairing reagent, was found to be an essential additive in obtaining a baseline separation. The resulting enantioseparative system was validated in order to evaluate the presence of the toxic l-penicillamine enantiomer in pharmaceutical samples.