The separation of cupric ions from aqueous solution by adsorption onto modified corncobs (hemicellulose-free) was studied. The adsorption process was found to take similar to 15 minutes to attain equilibrium in experiments with continuous agitation at 35 degrees C. The process was found to be pH-dependent, with increasing adsorption as pH increases up to 6.00. There is evidence that the adsorption mechanism is an ion-exchange one involving carboxylate groups, and that two binding sites may be present at the adsorbent. The adsorption was found to fit a Langmuir isotherm, and the parameters n(S) (adsorbent capacity) and b (adsorption intensity) were calculated. The results obtained show that corncobs are an interesting adsorbent because they are available in large quantities at several places in the world at little or no cost, and they retain cupric ions rapidly. The corncobs studied also contain aliphatic and phenolic hydroxyl groups that allow for the incorporation of other functional groups and thus increase the adsorbent capacity.