The molecular structures of three ethylanilines,ortho-,meta-and para-ethylaniline,have been obtained by means of Fourier-transform microwave spectroscopy.Rotational spectra of all three molecules display the nuclear quadrupole hyperfine structures arising from the 14N nucleus.Comparison of the determined structures allows a direct study of the influence of the position of the ethyl substituent on the structure of the amino group communicated through the phenyl ring.