Chemical polymerization of aniline in five different protonic acids, HCl, H2SO4, HBr, HNO3, and acetic acid (HAc), has been studied. the resulting polymers are characterized by elemental analysis, thermogravimetric analysis, infrared and x-ray photoelectron spectroscopy, and electrical conductivity measurements. It is found that a large fraction of the bromine and a smaller fraction of the chlorine in the product is covalently bonded. Thus a more accurate indicator of the degree of protonation would be the halogen anion rather than total halogen content. When H2SO4 is used for protonation, the anion incorporated in the polyaniline appears to be the HSO4- rather than the SO42- species. the degree of protonation of H2SO4 protonated polyaniline is significantly reduced when it is washed with water after the synthesis step. Treatment of the H2SO4, HBr, and HNO3 protonated polyaniline with HCl results in almost complete replacement of the respective anion by the chloride anion. the HBr protonated polyaniline sample shows partial solubility in CHCl3, with the insoluble fraction showing a slight improvement in conductivity after CHCl3 treatment.