The enzymatic polymerization of aniline to polyaniline (PANI) with Trametes versicolor laccase (TvL) as catalyst and dioxygen (O 2 ) as oxidant was investigated in an aqueous medium containing unilamellar vesicles with an average diameter of about 80nm formed from AOT (=sodium bis(2-ethylhexyl) sulfosuccinate). Compared to the same reaction carried out with horseradish peroxidase isoenzyme C (HRPC) as catalyst and hydrogen peroxide (H 2 O 2 ) as oxidant, notable differences were found in the kinetics of the reaction, as well as in the characteristics of the PANI obtained. Under comparable optimal conditions, which are pH 3.5 for TvL/O 2 and pH 4.3 for HRPC/H 2 O 2 , the reaction with TvL/O 2 was much slower than with HRPC/H 2 O 2 , i.e. ≈27 days vs. 1 day reaction time to reach equilibrium with >90% yield at 25°C. Although in both cases, aniline monomer coupling occurred mainly via the carbon atom in para position of aniline, UV–vis–NIR absorption and EPR measurements indicate that the reaction with TvL/O 2 yielded mainly overoxidized products (with λ max =730nm). These products had a lower amount of unpaired electrons if compared with the products obtained with HRPC/H 2 O 2 (with λ max ≈1000nm, which is characteristic for the polaron state of PANI-ES, the emeraldine salt form of PANI). Similarly to previous findings with HRPC/H 2 O 2 , enzyme inactivation occurred during the polymerization also in the case of TvL/O 2 . Since the aqueous PANI-vesicle suspensions obtained are of high colloidal stability, they can be used directly as ink in a conventional thermal inkjet printer for printing on paper or on surface treated polyimide films. Printed PANI-ES patterns on paper changed colour from green (emeraldine salt) to blue (emeraldine base) upon exposure to ammonia gas, demonstrating the expected ammonia sensing properties.