In the present study removal performance of 1-naphthol and 1-naphthylamine from wastewater by single and binary adsorption was compared. Synergistic effects were investigated in single-solute, binary-solute, and the preloading adsorption systems at 293 K. Two commercial polystyrene adsorbents Amberlite XAD-4, a macroporous adsorbent, and NDA-100, a hyper-cross-linked adsorbent, were employed here for their frequent use in organic pollutants removal front contaminated waters. All the adsorption isotherms of 1-naphthol and 1-naphthylamine on both adsorbents were found to be well represented by the Langmuir equation. Adsorption capacity of the primary solute was enhanced in the presence of the co-solute, arising presumably from the synergistic effect caused by the laterally acid-base interaction between the adsorbed 1-naphthol and 1-naphthylamine molecules. Due to the stronger adsorption affinity of 1-naphthylamine to nonpolar adsorbents, adsorption enhancement of 1-naphthylamine in the presence of 1-naphthol is greater than that of 1-naphthol in the presence of 1-naphthylamine. The greater synergistic effect of 1-naphthol/1-naphthylamine equimolar mixtures on XAD-4 than that on NDA-100 partly results front the larger average pore size of the former adsorbent. A modified extended Langmuir model is proved to well describe the synergistic adsorption of 1-naphthol/1-naphthylamine equimolar mixtures in the binary-solute system. The synergistic coefficient of one adsorbate is linearly correlated with the amount of the other adsorbed on the adsorbent. (c) 2008 Elsevier B.V. All rights reserved.