Spectra of the mesospheric OH(3,1) emission have been recorded by an FTIR spectrometer at Maynooth (53.2 degrees N, 6.4 degrees W), of Ireland on all suitable nights during the period December 1992 to July 1995. A total of 370 nights observations have been obtained. Each spectrum is acquired in a five minute integration period, and has been analyzed to yield a value of rotational temperature and brightness associated with the (3,1) band. Each of these measurements has been normalized to the mean value for the particular night on which it was recorded in an effort to extract the amplitude and phase of the variations. The normalized data have been binned at half-hourly intervals for each month so as to minimize the contribution to the variations from gravity waves and short period planetary scale oscillations. Harmonic analysis has been performed to determine an amplitude and a phase of both the diurnal and semidiurnal oscillations for each month in the period under study. The results of this investigation are presented and they are compared with the predictions of the theoretical model of Forbes and Gillette.