Adsorption of pyridine base molecules (pyridine and alpha-, beta- and gamma-picolines) on a surface of a natural zeolite, heulandite (0 1 0), was examined by Monte Carlo simulations. Two types of adsorption areas were identified on heulandite (0 1 0) bound by surface OH arrays, and each area showed different influence on the adsorption and orientation for pyridine base molecules. The presence of methyl group and its position within the adsorbed molecule also influenced its adsorption characteristics. For pyridine adsorption, molecular dynamics simulation was also performed. The results were compared with existing experimental data obtained through atomic force microscopy. (C) 2002 Elsevier Science B.V. All rights reserved.