Proteins were screened by preparing dispersions of SWNTs to investigate the driving force of the interaction between single-walled carbon nanotubes (SMINTs) of mean diameter I nm and water-soluble proteins. Egg white lysozyme (LYS) and bovine serum albumin (BSA) dispersed SWNTs, whereas papain and pepsin could not. Far-UV circular dichroism spectra indicated that the LYS and BSA molecules that coat SWNT surfaces were partially denatured. From the amino acid composition, we ascribed the main driving force to the hydrophobic interactions between the side-wall of the SWNT and the inner hydrophobic domain exposed to the solvent during the three-dimensional change of the protein induced by sonication. (c) 2006 Elsevier B.V. All rights reserved.