Since the discovery of mitochondrial ATP synthase subunit c storage in different forms of neuronal ceroid lipofuscinosis (NCL, Batten disease), it has been found that other hydrophobic proteins also accumulate in different forms. Costorage of subunit c of vacuolar ATPase is observed in "mnd/mnd" mice and in English Setters, Border Collies and Tibetan Terriers. A small amount is stored in the ovine disease and none in the human late-infantile disease. It is a storage body matrix component. An additional 8 kDa component immunoreactive to vacuolar ATPase subunit c antibodies is found in brain-derived storage bodies. The sphingolipid activator proteins, SAPs A and D, are stored in the human infantile disease and a form in Miniature Schnauzer dogs, but neither of the c subunits are. These results suggest two classes of NCL, the subunit c-storing diseases, related by a series of lesions in a subunit c-turnover pathway, and the SAP-storing diseases.