The aim of this project was to identify the gene mutation that causes ocular melanosis in Cairn terriers. This would allow us to develop a genetic test for breeders to use to allow them to eradicate ocular melanosis (OM) from their stock. Our initial approach was to use a genotyping microarray to try and identify the location of the gene mutation causing ocular melanosis. We performed this on DNA samples collected from both OM-affected and OM-unaffected Cairn terriers. This did not point to a particular region of the dog genome associated the ocular melanosis gene. Subsequently a high density genotyping microarray became available for the dog. We ran a new set of OM-affected and OM-unaffected DNA samples using the new microarray. These results have resulted in an apparent “hit” for the location of the OM gene. We are currently checking additional dogs for the region that the OM gene maps to so that we can verify the initial very promising findings. We are also sequencing the genes in the mapped region to see if any of them are altered in the OM-affected dogs. This has been a very significant step forward and we hope that it will lead to the gene mutation. However there is still a lot of work for us to do before we have a DNA test for Cairn terrier ocular melanosis.