29 kDa gold cluster molecules with thiol protection were synthesized and size separated by chromatography. Their direct laser desorption leads to large scale clustering and the mass spectral features extend up to 500 kDa. Effect of alkanethiol chain length on clustering suggests that monolayer interaction is the key to this phenomenon. Role of different matrices on clustering in the matrix assisted laser desorption ionization (MALDI) process has been investigated. (C) 2004 Elsevier B.V. All rights reserved.