The authors show an experimental setup to carry out soft-x-ray fluorescence spectroscopy of liquids under an ultrahigh vacuum (UHV) condition. The flow liquid cell has a window to attain compatibility with UHV conditions of the fluorescence spectrometer and synchrotron radiation beamline. The soft-x-ray photons enter the liquid cell through a 100 nm thick silicon nitride window, and the emitted soft x rays exit through the same window to be detected by photon diode and microchannel plate detectors. This setup allows liquids and, in particular, liquid-solid interfaces to be studied. Such a liquid cell has been used to study the electronic structure of a variety of systems ranging from water solutions of inorganic salts and nanomaterials under wet conditions. (c) 2007 American Vacuum Society.