Influences of solar UV variability on the total ozone column densities as measured by the total ozone mapping spectrometer (TOMS) on the Nimbus 7 satellite are investigated and distinguished from the noticeable signals of dynamical origin. We confine our analysis to the equatorial region where the purest observable periodic signals that relate to the solar UV variability at the solar cycle and solar rotational timescales appear. The Mg II index is used as a proxy for solar variability in the UV region of the solar spectrum. Applying a multiple taper method of power spectral estimation to the entire TOMS observation period (14.4 years), evidence for a solar cycle variation is obtained at the 95% confidence level. The estimated solar cycle variation is 1.5¿0.3% from solar minimum to maximum, corresponding to a 7.6¿0.7% change in the Mg II index with no significant phase lag. The most significant line contributions to the power spectrum of the daily total ozone values in the proximity of solar rotation frequencies have periods of 28.4¿0.2 and 14.6¿0.1 days during maximum solar activity in solar cycle 22. F tests show both lines to be significant at or above the 99% level. Identical analysis of the Mg II index for the same period shows the strongest signals appearing at 28.4¿0.5 and 13.5¿0.1 days. The latter signal is more difficult to confirm because of possible interference with other lines at close frequencies (14.8 and 12.3 days). The sensitivity of total ozone to the major solar rotational mode is comparable to the solar cycle effect, and the results are consistent with solar signals of pure photochemical origin. Strong coherency appears in a couple of narrow frequency bands around 26 and 13 days showing that total ozone responds to solar UV radiation in both of the major solar rotation modes.¿ 1997 American Geophysical Union