Aggregated structures of N-methylacetamide in 1,4-dioxane solution have been studied using infrared electroabsorption spectroscopy. Predominance of two structures, the monomer and dimer, is demonstrated. For the monomer, angles alpha between the permanent dipole moment and the transition dipole moments are determined to be 6degrees +/-9degrees for the amide A, 0degrees +/- 13degrees for the amide I, 62degrees +/- 4degrees for the amide II modes, respectively. For the dimer, the experimental results are explained very well by assuming a head-to-tail structure, which has the permanent dipole moment twice as large as that of the monomer and similar alpha values as those of the monomer. (C) 2002 Elsevier Science B.V. All rights reserved.