anodic surface treatment of high tensile-carbon fibers under galvanostatic conditions has been performed in diammonium hydrogen phosphate solution, containing an addition of ammonium rhodanide. the oxidized fibers have been characterized by monofilament tensile strength, xps measurements and surface energetic analysis. in addition, the acid-base interactions have been evaluated by wetting with aqueous solutions with different ph values. an addition of ammonium rhodanide to the diammonium hydrogen phosphate anodization bath affects the oxidation of carbon fibers by decreasing both the amount of the surface oxides as well as the amount of degradation byproducts. under the optimal treatment conditions (i $equals$ 100 ma) no changes in the tensile strength or bet surface area of the fiber have been observed. the rise in interlaminar shear strength values of amine-cured epoxy composites is not dependent on the o//1//s/c//1//s ratio or surface free energy of the reinforcing fibers, but on the acidic as well as nitrogen functional groups on their surface. (edited author abstract) 17 refs