The deposition of ozone to seawater is known to be controlled by a variety of physical and chemical processes. At low wind speeds chemical loss is comparatively more important than loss due to physical processes. We have determined experimentally the relationship between ozone deposition velocity and concentration of iodide and dissolved organic matter in water buffered at seawater pH (8.0). The concentrations of both species used in this study are representative of those encountered in coastal and oceanic systems. We show that dissolved organic matter and iodide contribute to a similar degree to the chemical enhancement of ozone deposition to surface waters.