We studied 25 infants aged less than 9 months who were diagnosed as having nonpolio enteroviral meningitis (EM) confirmed by virus isolation from cerebrospinal fluid (CSF). CSF protein, glucose and cellular content in these infants was compared with that of 125 age-matched febrile infants without cerebromeningeal illness. In order to control for changes occurring in the CSF during the first 2 months of life, the studied infants and the control subjects were stratified into 2-week age-groups and were compared. All but three of the infants with EM had increased CSF leukocyte count, and 10 infants showed domination of the polymorphonuclear leukocytes in the CSF. Only two had increased CSF protein levels, and low CSF/blood glucose ratios were found in all but two cases. None of the infants with EM had increased values of CSF protein concomitant with decreased CSF/blood glucose ratio. CSF in EM is characterized by increased white blood cell count in contrast with normal or near-normal CSF protein and glucose levels. In some infants, enterovirus isolation may be the only evidence of EM.