The lower stratospheric variability of equatorial water vapor, measured by the Microwave Limb Sounder (MLS), follows an annual cycle modulated by the quasi-biennial oscillation. At levels higher in the stratosphere, water vapor measurements exhibit a semiannual oscillatory signal with the largest amplitudes at 2.2 and 1 hPa. Zonal-mean cross sections of MLS water vapour are consistent with previous satellite measurements from the LIMS and SAGE II instruments in that they show water vapor increasing upwards and polewards from a well defined minimum in the tropics. The minimum values vary in height between the retrieved 46 and 22 hPa pressure levels. ¿ American Geophysical Union 1995