Acute metabolic crisis occurring in 7 children (6 at ages 3-9 months, and 1 at 5 years), between 3 and 12 hours after administration of Japanese encephalitis, diphtheria, and tetanus toxoids, and acellular pertussis, hepatitis B, and measles vaccines, is reported from Peking University First Hospital, Beijing, China. Preexisting primary diseases, not known before vaccination, included Leigh disease in 3 infants, glutaric aciduria type 1, methylmalonic aciduria, and 21-hydroxylase deficiency in one 3 month old and one previously diagnosed 5 year old. Four patients were previously healthy, and suffered fever, seizures, coma, acidosis, and hypoglycemia soon after vaccination, all succumbing to respiratory failure before 2 years of age. Symmetric foci, cystic cavitations with neuronal loss, and vascular proliferation were found at autopsy. 
COMMENT. One patient had a family history of infantile deaths and was diagnosed with congenital adrenal hyperplasia and 21-hydroxylase deficiency before vaccination. A second patient subsequently diagnosed with 21-OH deficiency was malnourished in infancy, and a 3 month-old with methylmalonic aciduria was hypotonic. The remaining 4 infants appeared normal before vaccination. Vaccination in infants with unrecognized metabolic disorders carries a risk of metabolic crisis. Infants who are malnourished, slow in development, hypotonic or have symptoms suggesting a metabolic disorder should receive appropriate laboratory tests before vaccination.