Ozone flux measurements over vegetation are important to estimate surface losses and ozone uptake by plants. The gradient and eddy covariance flux technique were used for measurements over grassland at a flux-monitoring site in southern Scotland during August 2007. The comparison of the two methods shows that the aerodynamic flux-gradient method provides very similar long-term average fluxes of ozone as the eddy covariance method. The eddy covariance technique is better at capturing diurnal cycles and short-term changes, but the comparison of two fast analysers illustrate that there can be considerable measurement uncertainty. Copyright © 2009 Royal Meteorological Society