The uptake of inorganic Hg2+ and organometallic CH3Hg+ from aqueous solutions by 11 different natural zeolites has been investigated using a batch distribution coefficient (K
d) method and supported by a preliminary voltammetric study. The effect of mercury concentration on the K
d response is shown over an environmentally appropriate concentration range of 0.1–5 ppm inorganic and organometallic Hg using a batch factor of 100 ml g-1 and 20 h equilibration. Analcime and a Na-chabazite displayed the greatest methylmercury uptakes (K
d values at 1.5 ppm of 4023 and 3456, respectively), with mordenite as the smallest at 578. All uptake responses were greater for methylmercury than for the inorganic mercuric nitrate solutions, suggesting a distinctive sensitivity of zeolites to reaction with different types of solute species. It is likely that this sensitivity is attributable to the precise nature of the resultant Hg-zeolite bonds. Additionally, both the Si-Al ratio and the Na content of the initial natural zeolite samples are shown to influence the K
d responses, with positive correlations between K
d and Na content for all zeolites excluding mordenite.