The mass and surface changes produced when a commercial activated carbon is treated with HNO3 solutions and in the subsequent heat treatment of the resulting samples are investigated. In the preparation of samples, acid solutions of varying concentration were used. The outgassing, first of activated carbon, and the contact, then of the acid solution with the resulting intermediate product, were effected under controlled temperature and temporal conditions. The starting carbon and some HNO3-treated samples were examined by Fourier transform-infrared spectroscopy. Brunauer-Emmett-Teller (BET) surface areas were determined by nitrogen adsorption at -196 degrees C. Heat treatments were carried out between 30 degrees and 800 degrees C in nitrogen. The oxidation of the activated carbon resulted in a significant mass increase. This was dependent on the method of preparation of the samples. Also, the surface chemistry of the activated carbon modified. Additionally, the surface area of the carbon underwent slight changes, this textural parameter increasing for a number of samples. The mass loss in the heat treatment of the samples was higher than the mass gain produced in their preparation. The mass loss was greater in the 30 degrees-180 degrees C range than in the 180-500 degrees and 500-800 degrees C ranges. In the various temperature ranges, the mass loss generally increased with increasing concentration of the HNO3 solution and the outgassing and contact temperature or time.