AbstractTwo acid‐resistant fractions were isolated from three soils, a Sims clay loam, a Houston Black clay, and a Xenia silt loam. The fractions were separated by paper electrophoresis and analyzed for functional groups by infrared spectra. One component was a dark‐colored nonfluorescent material and the other a yellow fluorescent water‐soluble material. Chemical analysis of the darker humic acid obtained from the Xenia silt loam gave the following results: C, 52.48%; O, 38.38%; H, 4.65%; N, 1.98%. This material was found to contain 6.7% methoxy groups. Infrared spectra of the two fractions showed them having a different structure, but both materials were throught to contain hydroxyl and carbonyl groups. The N content of the dark‐colored fraction separated by electrophoresis was 1.98% for the Xenia and Sims soils and 1.79% for the Houston soil. Because of the similarity of these materials in infrared spectra and N content, it is believed that these acids are of fundamental importance in the structure of soil organic matter.