As the first step for full assignment of infrared (IR) active vibrational modes in crystalline triacylglycerols (TAGs), methylene wagging and rocking regions of beta-forms of a series of monoacid TAGs having C10 through C22 acids were investigated. The wagging region was especially complicated, because dispersion curves of methylene wagging (nu(3)) and twisting-rocking (nu(7)) modes were overlapped and the three acyl chains of TAGs exhibited their own IR bands. In order to resolve the complicated spectra of TAGs, three polarized IR techniques (oblique transmission, attenuated total reflection, and reflection-absorption spectroscopy) were employed in addition to the ordinary transmission method, and the obtained spectra were compared with those of a series of monoacid 1,3-diacylglycerols. It was found that the two straight sn-l and sn-2 chains of monoacid TAGs showed different series of IR progression bands from those of the bend sn-3 chain having a gauche bond in the neighborhood of the ester bond. The nu(7) modes of the bend chain made a significant contribution to the CH2 wagging region as well as the nu(3) modes of both the straight chains and the bent chain.