The adsorption of methylene blue (MB) on three commercial granular activated carbons (GACs), 12 x 40 mesh size, namely Filtrasorb 400, Norit and Picacarb has been researched. A comparative Study adsorptive capacity using the proposed single-point test and the traditional multi-point isotherm test was carried Out. For the single-point test, the influence of some parameters Such as MB/GACs mass ratio and contact time were evaluated. For this test the adsorptive capacities of the three GACs studied were 319 +/- 14, 280 +/- 7 and 260 +/- 6 mg g(-1) for Filtrasorb 400, Norit and Picacarb, respectively. For multi-point isotherm adsorption test the Langmuir model was used. The parameters involved were obtained by linear and non-linear regression methods. The Maximum adsorptive capacity values obtained for both methods were similar and statistically not different than those obtained with the single-point tests. This experimental work also aimed at establishing a relationship between the adsorbent particle size and the adsorptive capacity which Could be used complementarily to evaluate the quality of GACs as adsorbents. For a mean particle diameter of 1 mm and after 24 h of contact time the adsorptive capacity values were 255 +/- 7, 222 +/-7 and 160 +/- 7 mg g(-1) for Filtrasorb 400, Norit and Picacarb, respectively. (C) 2008 Elsevier B.V. All rights reserved.