Flue gases from a hazardous waste incinerator have been sampled in three campaigns, before and after, an oxidative acid wet scrubber working with the Merc-Ox-process. A continuous emission monitor for mercury speciation was used before the scrubber in the first campaign. In all campaigns, impingers with KCl and KMnO4 were used. A solid adsorption method was used in the last campaign. The mercury leaving the scrubber is oxidized at > 90 % efficiency (independent of the inlet speciation). A substantial decrease in the redox potential of the scrubber liquid caused an increased fraction of elemental gaseous mercury to be present in the clean gas. The measurements also show that the scrubber has the 3 ability to readily absorb mercury peaks. During one extreme peak of 3,600 mu g/m(3) (dry gas) in the raw gas, the removal efficiency was above 99.9%.