Five patients with juvenile neuronal ceroid-lipofuscinosis, who were shown to have absent or reduced serum prebetalipoprotein and a deficiency of polyunsaturated fatty acids in erythrocyte membrane lipids, were treated for a period of one year with supplements of fish oil extract (rich in omega-3 fatty acids) and encouraged to increase dietary intake of corn oil lipid (rich in omega-6 fatty acids) in an attempt to promote incorporation of these fatty acids into membranes. After one year there was a significant increase in omega-3 fatty acids (P less than 0.05) and in the total polyunsaturated fatty acids (P less than 0.02) in erythrocyte membranes but no change in the incorporation of omega-6 fatty acids. The patients were assessed clinically, psychometrically and neurophysiologically before and after the supplementation. No significant changes were noted after one year of treatment.