The first year-round observations of seasonal and diurnal variations of background ozone at a coastal site on Crete Island in the southeast Mediterranean area are presented here. They point out (1) the existence of a well-defined seasonal cycle with maximum during summer months, (2) the presence of elevated O3 levels (up to 80 ppbv) during daytime and over time periods of several days, and (3) the dependence of O3 mixing ratios on air mass origin. Comparison with three-dimensional chemistry transport model results shows that during summer the measured O3 values exceed the calculated by 10-20 ppbv. Inclusion of biomass burning and biogenic volatile organic emissions in the model could partly offset the discrepancy between model results and observations. ¿ 2000 American Geophysical Union