Poly(aniline-co-o-toluidine) and poly(aniline-eo-m-toluidine) have been synthesized by both chemical and electrochemical copolymerizations of aniline with o-toluidine and with m-toluidine, respectively. The compositions of the copolymers were determined by1H NMR spectroscopy and could be altered by variation of the comonomer feed ratios. Thus, conductivity of copolymers can be controlled in a broad range, (e.g. when doped with 1 M HC1), from ca. 10 S/cm for homopolymer of aniline to ca. 0.1 S/cm for those of toluidines. The relationship between copolymer composition and comonomer feed ratio shows that the toluidines are more reactive than aniline in the copolymerization. The results are consistent with the proposed mechanism for the polymerization of aniline and its derivatives. © 1990, American Chemical Society. All rights reserved.