We describe two male infants with central nervous system disorders, i.e. infantile spasms in one and athetotic quadriplegia in the other, and with recurrent attacks of high plasma creatine kinase levels induced by viral infections. Although carnitine palmitoyltransferase I (CPT I) activity in biopsied muscle was normal in both cases, that of carnitine palmitoyltransferase II (CPT II) was decreased to 37% and 25% of the control value, respectively. Meanwhile, to determine whether or not and how CPT exists in the central nervous system (CNS), we studied animal brain tissues. CPT activity was demonstrated in almost all regions, especially in the brainstem, cerebellum and spinal cord. Although CPT deficiency can be classified into hepatic (CPT I) and muscular (CPT II) presentations, these data suggest that another symptomatology of CPT II deficiency with CNS involvement (brain type?) might exist.