A matrix-free laser desorption method combined with supersonic jet-cooling is developed to produce clusters of the nucleobases and their hydrates. The cooling characteristics and hydration efficiency of this method are investigated by using two types of desorption sources. It is demonstrated that guanine clusters can be formed at low effective temperatures by using a channel-type desorption source. This desorption method is also found to produce hydrated guanine clusters with high efficiency with respect to conventional desorption methods. Dependence of the desorbing wavelength on the desorption efficiency is also investigated. (c) 2005 Elsevier B.V. All rights reserved.