This paper presents a study of the equatorial diurnal tide at 27--55 km based on temperature data from the Upper Atmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS). The MLS temperature retrieval is significantly improved in the lower stratosphere with the recent (version 4) software and able to provide useful tidal information down to 22 hPa. The diurnal amplitude and phase, derived from MLS ascending-descending temperature differences, show a strong annual variation in the lower stratosphere and a semiannual variation in the upper stratosphere and mesosphere, which are in good agreement with other UARS measurements and simulations from the Canadian Middle Atmosphere Model (CMAM). The largest differences between the observation and the model appear at 22 and 1 hPa, reflecting some shortcomings in current tidal modeling. It is shown in MLS observations that the (1,1) tide suffers severe reduction in amplitude at 1 hPa which could be caused by the interference between the propagating tide and the component generated by stratospheric ozone heating. The data also indicate the possible presence of a short-lived propagating component (i.e., the (1,2) mode) in the lower stratosphere, which can be excited in the upper troposphere but damped quickly as it propagates upward. ¿ 1998 American Geophysical Union