The Global Ozone Monitoring Experiment (GOME) flown onboard ERS-2 satellite has been providing vertical columns of ozone and NO2 routinely since July 1996. Those level 2 products, as well as total ozone measured from space by two NASA's Total Ozone Mapping Spectrometers (TOMS), have been compared to ground-based colocated observations of the Network for the Detection of Stratospheric Change (NDSC) and of the SAOZ/UV-visible network. Comparisons with each space-borne sensor have been combined altogether for investigating the solar zenith angle (SZA) dependence, the dispersion and the difference of sensitivity of the space instruments. The present paper summarises the current conclusions on the quality of GOME level-2 products. The GOME and ground-based total ozone agree within a few percent on average. However the analysis demonstrates a clear dependence on the SZA and the ozone column. The preliminary validation of the GOME total NO 2 and 'near-real-time' ozone profiles is also reported.