Self-assembled monolayers of methyl(1-mercaptoundec-11-yl)tri(ethylene glycol) (CH3O(C2H4O)(3)C11H22SH, EG3-OMe) adsorbed on gold were investigated by IR-vis sum frequency generation in the range of the C-H stretching vibrations. Comparison of the monolayers in ambient atmosphere, in contact with water, and in contact with carbon tetrachloride revealed that the film structure is strongly disturbed by the interaction of the liquid with the monolayer. The ordered structure found in air undergoes an amorphization upon exposure to the solvents. The experiments demonstrate that in situ analysis of the film structure is mandatory.