Mesospheric ozone and temperature data obtained by the Microwave Limb Sounder (MLS) on board the Upper Atmosphere Research Satellite (UARS) have been analyzed to elucidate quasi-two day wave activity. Data from January 1993 were analyzed to investigate the evolution and structure of the two day wave. During this period, the wave amplitude in ozone attained its maximum value in late January near 30¿ in the summer hemisphere. The evolution of the wave amplitude indicates a shift of the peak amplitude to higher latitudes with increasing height. Correlation of the two day wave phase observed in MLS ozone and temperature measurements indicates that the perturbations are out of phase. During the same period, the amplitudes of the perturbations in temperature and ozone were positively correlated. The results suggest that the variations in ozone are photochemically driven in the mesosphere region via changes in reaction rates that are strongly temperature dependent. ¿ 2001 American Geophysical Union