The histopathological and ultrastructural findings in the central nervous system and lymphoid tissue of Abyssinian kittens suffering from a disease which was clinically characterised by neurological disturbances, are described. The lesions were vacuolisation of neurones and macrophages with light microscopy and lamellated membranous cytoplasmic bodies, initially in lysosomes with electron microscopy. Irregularly shaped membrane-bound bodies with an amorphous substance were eventually formed in the cytoplasm of affected cells. It is considered that this is a lysosomal storage disease.