Ultrathin (1-10 layers) aniline and pyridine films deposited on a Ag(111) surface at 90 K have been examined using thermal programmed desorption (TPD). Multiple desorption peaks have been observed for both systems showing film growth from the first chemisorbed layer to the bulk structure through multiple intermediate layers. The growth mechanisms for the two systems are, however, apparently different. Aniline films are formed one layer at a time with five thermodynamically stable layered structures. In contrast, pyridine films grow through metastable phases, similar to benzene film deposition on metal. In particular, a skin layer over the bulk phase is proposed to account for the TPD spectra. The difference in film growth mechanisms is attributed to the effect of intermolecular interactions.