Copolymers of metanilic acid (MA) and aniline (An) were electrodeposited by cyclic voltammetry from dilute H2SO4 containing 0.1 M of MA and varying amounts of An. The MA content in the copolymers was determined by Fourier transform IR (FTIR) and UV-visible analyses of spectral features attributable to MA. It is found that the MA content decreases with film thickness, and with increasing acidity and An concentration in the depositing solutions. The results are interpreted in terms of the limited involvement of MA monomers in copolymerization, particularly in the late stage of polymer growth. The presence of MA units in copolymers are not detectable at An/MA ratios approaching unity. Although MA monomers are incorporated only sporadically, extended polymer growth is inhibited even by trace quantities of MA because of the unfavourable combination of inductive and steric effects imposed by the bulky sulphonate pendant groups.