We present a theoretical study of the vertical electronic excitation energies of the alanine zwitterion in an aqueous environment. The study is based on calculations using the combined coupled cluster/molecular mechanics (CC/MM) method. The CC/MM results (using different water potentials) are compared to calculations based on density functional theory (DFT) using the B3LYP functional. Special attention is payed to the lowest n(O) -> pi(*)(CO) transition and higher lying states including the pi(CO) -> pi(*)(CO). We find that the spectra obtained using CC/MM are in good agreement with experiments. On the other hand, less satisfactory results are found for the spectrum calculated using DFT. (c) 2006 Elsevier B.V. All rights reserved.