Copper toxicosis in Bedlington Terriers is an autosomal recessive condition characterized by high levels of hepatic copper. The disease usually leads to liver damage and cirrhosis. Most Bedlington populations show a high incidence for this condition. Testing is currently carried out by histological examination and measurement of copper levels in liver biopsies (for affected dogs) or by using a microsatellite marker (C04107) in a PCR-based test. Uncertainties in interpretation of these tests make development of a DNA-based test detecting the causative mutation a priority. Recent studies identified the mutation as a deletion of exon 2 in the gene MURR1 and also showed that C04107 is situated within intron 1 of this gene. Research at the Animal Health Trust has subsequently characterized the mutation precisely and will provide the basis for developing a new test. We propose a limited study to develop a robust diagnostic test from our research data on MURR1. PCR multiplexes developed for research will be adapted for use on an ABI 3100 sequencer for high-throughput routine testing. The testing protocol will be optimized using a set of samples from dogs which we have already typed for C04107, containing a representative mix of C04107 genotypes.