The adsorption of the heavy metal ions Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ from aqueous solution by used coffee grounds has been investigated as a potential low-cost treatment method for heavy metal-containing waste waters that is based on a readily available natural by-product. The results show that metal ion adsorption is efficient over a fairly wide pH range and adsorbed metals are reversibly leached from the exhausted coffee by dilute acid without significant loss of the adsorptive capacity for subsequent re-use. [DOI: 10.1380/ejssnt.2006.504]