Ozone profiles measured by two satellite instruments (GOME-2A and OMI) have been combined with a chemical transport model using data assimilation. The results give a better insight into the global spatial and temporal ozone distribution than either measurement or model results alone. Validation with independent measurements shows biases varying between -5 % and +10 % between the surface and 100 hPa, while between 100 and 10 hPa the biases vary between -3 % and +3 %.