Ozone variability in the equatorial middle atmosphere is investigated and related to temperature and zonal wind variations using data from the Nimbus 7 and Solar Mesosphere Explorer (SME) satellite. The dominant component of the seasonal variability at most levels from the middle stratosphere to the lower thermosphere is the semiannual oscillation (SAO) which has maxima near 10, 3, 0.07, 0.01 mbar, and near or above 0.0024 mbar. There is evidence that the 10-mbar peak is due to vertical advection of odd nitrogen (NOy) by the semiannually varying residual mean circulation, while temperature dependence of chemical reactions coupled with the thermal SAO near the stratopause and in the upper mesosphere is responsible for the peaks near 3 and 0.07 mbar. The seasonal dependence suggests a contribution from gravity wave modulated vertical mixing of water vapor near the 0.01 mbar level, and we speculate that semiannually modulated mixing of atomic oxygen by the (1,1) mode of the thermal tide contributes to the SAO ozone peak above 0.0024 mbar. The negative correlation between temperature and ozone is so strong in the 7- to 0.5-mbar layer that ozone is a useful proxy for temperature variability on time scales from a few days to many months. A preliminary look at annual and interannual variations shows that differing patterns of winter high latitude Rossby wave variability in the two hemispheres are reflected in the signature of equatorial ozone and temperature in the same layer. ¿ American Geophysical Union 1990