Peanut shells of mesh size 10-20 were modified by combinations of treatments following a 3(2) factorial design. Treatments consisted of either no wash, water wash or base wash followed by no modification or modification with 0.6M citric acid or 0.6M phosphoric acid. The nine samples were evaluated for their uptake of five metal ions (Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II)) from solution. The results were compared with metal ion adsorption by three commercial cation exchange resins, namely, Amberlite(R) 200, Amberlite(R) IRC 718 and Duolite(R) GT-73. The percent of metal ions adsorbed per gram of adsorbent was significantly increased by each of the acid treatments, average values ranged from 19 to 34% compared with non-acid treated samples at 5.7%. The percent of metal ions adsorbed for base-washed samples were higher than water-washed or unwashed shells. Interaction between wash and acid treatment was not significant for most of the experimental conditions used. Acid-treated samples were as effective as Duolite(R) GT-73 in the adsorption of Cd(II) and almost twice as effective in the adsorption of Zn(II) from solutions containing a single metal ion. In solutions containing multiple metal ions, citric acid samples were found to be most effective and selective for Cu(II) compared with Cd(II), Ni(II), and Zn(II). In general, phosphoric acid-modified shells removed the most metals from solution for the experimental samples and were more effective in removing Cd(II) and Zn(II) than two of the three commercial resins. Acid-modified peanut shells are promising as metal ion adsorbents.