The influence of molecular oxygen in the interactions of emeraldine base form of polyaniline (EB-PANI) with Fe(III) or Cu(II) ions in 1-methyl-2-pyrrolidinone (NMP) solutions has been investigated by UV–vis–NIR, resonance Raman and electron paramagnetic resonance (EPR) spectroscopies. Through the set of spectroscopic results it was possible to rationalize the role of O2 and to construct a scheme of preferential routes occurring in the interaction of EB-PANI with Fe(III) or Cu(II). Solutions of 4.0mmolL−1 EB-PANI with 0.8, 2.0 and 20mmolL−1 Fe(III) or Cu(II) ions in NMP were investigated and the main observed reactions were EB-PANI oxidation to pernigraniline (PB-PANI) and EB-PANI doping process by pseudo-protonation, or by a two-step redox process. In the presence of O2, PB-PANI is observed in all Fe(III)/EB solutions and EB-PANI doping only occurs in solutions with high Fe(III) concentrations through pseudo-protonation. On the other hand, emeraldine salt (ES-PANI) is formed in all Fe(III)/EB solutions under N2 atmosphere and, in this case, doping occurs both by the pseudo-protonation and two-step redox mechanisms. In all Cu(II)/EB solutions PB-PANI is formed both in the presence and absence of O2, and only for solutions with high Cu(II) concentrations doping process occurs in a very low degree. The most important result from EPR spectra was providing evidence for redox steps. The determined Cu(II) signal areas under oxygen are higher than under N2 and, further, the initial metal proportions (1:2:20) are maintained in these spectra, indicating that Cu(I) formed are re-oxidized by O2 and, so, Cu(II) ions are being recycled. Consistently, for the solutions prepared under nitrogen, the corresponding areas and proportions in the spectra are much lower, confirming that a partial reduction of Cu(II) ions actually occurs.