A comparative study of the conductivity behavior of methane-sulfonic acid solutions of poly(p-phenylene-cis-benzobisoxazole) or cis-PBO and other compounds, including CH3SO3Na (NaMSA), a cis-PBO model compound, and 6,7-dimethyl-2,3-di(2-pyridyl) quinoxaline, a molecule containing four protonating sites, was carried out to determine the degree of protonation of PBO and its model compound. The conductivity dependence with increasing cis-PBO concentration indicates that only two sites per repeat unit are protonated.