Poly(N-methylaniline) (PNMeANI), poly(N-ethylaniline) (PNEtANI), poly(N-propylaniline) (PNPrANI) and poly(N-butylani-line) (PNBuANI) films were polymerised on glassy carbon and tin oxide (TO) substrates in 1.0 M HClO4. The pH sensitivity of the polymer films was investigated with potentiometry and UV-vis measurements in aqueous buffer solutions with pH 2-9. The results of these measurements were compared with polyaniline (PANI) prepared in 1.0 M HCl In this study, the potential and the UV-vis spectrum of the different polymer films deposited on TO were measured simultaneously. These optopotentiometric measurements give information about the surface and bulk processes in the N-substituted polyaniline films when they are in contact with the buffer solutions of different pH. It was shown that the N-substituted polyaniline films were not pH sensitive. The suppressed potentiometric pH sensitivity of the N-substituted polyanilines, which were observed when changing pH, are caused by reduction of the polymer films from their emeraldine to leucoemeraldine oxidation state. Polymerisation of PNMeANI in 0.1 M dodecylbenzenesulphonic acid (DBSA) solution is also reported in this paper.