A screening procedure is described to assess rapidly the clinical potential of chelating agents for the treatment of Wilson's disease. 2. Rats were used as the test animal; they were kept in metabolic cages and the urine was collected in copper-free containers. The compounds investigated were given by mouth as a standard dose of 100 mg. Copper was determined by atomic absorption spectrophotometry. 3. Basal urine copper excretion was 65-1 +/- SE 2-93 nmol/24 h (4-1 microgram +/- 0-185). After penicillamine this rose to 367-1 nmol and after trien to 305-9 nmol. 4. Certain compounds caused a reduction in the amount of copper excreted in the urine, probably by forming insoluble chelates with the metal, hence rendering it unavailable for excretion at the glomerulus.