In the present work we discuss the interactions between an armchair (5, 5) single walled carbon nanotube (SWNT) and amino acids. After multiple configurations and test calculations we have deduced that the highest dissociation energies are obtained when metallic SWNT systems interact with biological molecules. The DFT-BLYP/DND calculations reveal that the most favorable interactions of the SWNT system is with arginine, cysteine, alanine and asparagine which is related to the backbone structure of the corresponding amino acids. (C) 2008 Elsevier B.V. All rights reserved.