The interaction of emeraldine base polyaniline (EB) with Cu(II), Fe(III), and Zn(II) in 1-methyl-2-pyrrolidinone (NMP) solution was monitored using electronic UV-vis-NIR, resonance Raman, and electron paramagnetic resonance (EPR) spectroscopies. The films prepared from these solutions were also spectroscopically characterized. It was demonstrated that the nature of the products (semiquinone and quinone segments) formed from the interaction of EB and metal ions is strongly dependent on the nature of the cation, the metal/EB molar ratio, and the concentration of the components. The presence of semiquinone segments (radical cation) in EB solutions with Cu(II) and Fe(III) was undoubtedly confirmed by the observation of an electronic absorption band at ca. 900 nm, a characteristic Raman band at ca. 1330 cm(-1) (nu(C-N.+)), and also an EPR signal at g = 2.006. The influences of metal/EB molar ratio and metal ion concentration on the formed species were investigated in Cu(II) and Fe(III) solutions, and it was verified that diluted solutions favor the formation of oxidized segments (pernigraniline) instead of doped ones (emeraldine salt). No matter the nature of metal ion solutions, all the polymeric films show a spectroscopic behavior of ES (doped polymer) according to electronic and Raman spectroscopic data.