Self-assembled (SA) and Langmuir-Blodgett (LB) monolayers of nonadecanoic acid on the surface of silver have been investigated by reflection-absorption Fourier transform infrared spectroscopy. The molecule was chemisorbed on silver very favorably as nonadecanoate after losing the carboxylic proton. Although both the LB and SA monolayers consisted of fully extended trans zigzag molecular chains assembled in a crystalline state the carbon chains of SA monolayers seemed to assume a more perpendicular stance with respect to the silver surface than those of LB monolayers.