The doping process in a recently developed conducting polymer precursor, poly(3,4-diisopropylidenecyclobutene) (PDPCB) was studied by ESR and optical spectroscopy. Thin films of PDPCB were exposed to several oxidants, I2, AsF5, or a combination of AsF5 and AsCl3 or AsF3, and monitored in situ by ESR. At the initial stages of doping, the films developed broad ESR spectra with a Gaussian line shape. Except in the case of doping with I2, resolved hyperfine structures from cation radicals were obsd. As the doping progressed, the ESR spectra gradually transformed to narrower line widths with a Lorentzian component. The Lorentzian component can be attributed to charge carrier species developed in the film through doping. The results of optical spectroscopy (UV-visible) are incorporated to elucidate the effect of doping on electronic transitions of the doped PDPCB. [on SciFinder(R)]