The human hereditary ceroid-lipofuscinoses are a group of autosomal recessively inherited diseases characterized by massive accumulations of autofluorescent lysosomal storage bodies in the cells of many tissues and by neuronal degeneration throughout the central nervous system. There are a number of clinically and genetically distinct forms of ceroid-lipofuscinosis, the most common of which is the juvenile type, also known as Batten disease and CLN3. To study the mechanisms that lead to pathology in CLN3 and to evaluate potential therapies, a mouse model has been generated by targeted disruption of the mouse ortholog of the CLN3 gene (Cln3). As in affected humans, mice homozygous for the disrupted Cln3 allele show accumulation of autofluorescent storage material in neurons and other cell types. The storage material consists of membrane-bounded intracellular inclusions with ultrastructural features typical of the ceroid-lipofuscinoses. The accumulation of this storage material validates the Cln3 knockout mice as a model for the human disorder.