Droplet-beam laser-ablation mass-spectrometry was applied for a study of the UV-laser induced proton-transfer reaction of protonated lysozyme hydrated clusters in the gas phase. Protonated lysozyme hydrated clusters were produced by irradiation of an IR laser onto a droplet-beam of an aqueous solution of lysozyme and were subsequently irradiated by a UV laser. It is found that H+ and H3O+ are produced through photodissociation of protonated lysozyme hydrated clusters. The mechanism of the proton-transfer reaction is discussed. (c) 2008 Elsevier B.V. All rights reserved.