The neuronal ceroid lipofuscinoses (NCLs) are lysosomal storage diseases with severe neurodegenerative pathology. An ovine model (OCL) has well defined parallels with the human disease at a biochemical and pathological level. The gene for OCL is located in the chromosomal region OAR 7q13-15. This region is syntenic with HSA 15q21-23 suggesting that OCL and CLN6 represent mutations in orthologous genes. New microsatellite markers were used for refinement of the OCL critical region. YAC clones that span the critical region have been isolated and comparative gene mapping confirms that the regions for CLN6 and OCL are equivalent.