Results of international experiments for the validation of measurements of total ozone content (TOC) by the GOME instrument are reviewed and compared with measurements made with independent surface measurements from Dobson and Brewer spectrophotometers and the M-124 ozonometer. The results of numerous comparisons of on-line GOME TOC data with data from ground-based measurements by the Russian ozone monitoring network during 1996-2000 reveal that the GOME data systematically understate TOC (by 4-9%), also noticeable in comparison with data from simultaneous TOMS measurements.