Four data assimilation systems have been working extensively on MIPAS ozone data. These are: DARC, ECMWF, GMAO and BASCOE. All assimilations systems were prepared to contribute to the CAL/VAL workshop. The MIPAS data are version 4.61. The Data Assimilation Research Centre (DARC), European Centre for Medium - Range Weather Forecasts (ECMWF) and the Global Modelling and Assimilation Office (GMAO), assimilated MIPAS ozone data in addition to other observations containing ozone information. BASCOE (Belgian Assimilation System of Chemical Observations from Envisat) assimilated only MIPAS observations. The overall findings are a better MIPAS ozone quality, with less contaminated data. The MIPAS data lead to an overall improvement of the ozone analyses with respect to independent data.