Plasma polymers of acrylic (propenoic) acid and propanoic acid were prepared from inductively coupled, radio-frequency-induced plasmas excited in vapors of the starting materials. The plasma polymers were characterized by X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRAS), and static secondary-ion mass spectrometry (SIMS). Detailed interpretation of the spectra allows determination of the distribution of chemical functionalites at the surface of the product and of the influence of unsaturation and plasma power on this distribution. The results are discussed in the context of previously proposed mechanisms of plasma polymerization of the compounds under investigation.