Differentiation of bacterial from aseptic meningitis may be difficult. Our aim was to determine the pattern of distribution of lactate dehydrogenase (LDH) isoenzymes in the cerebrospinal fluid (CSF) of patients with bacterial and aseptic meningitis. One hundred and fifty-seven patients with suspected meningitis were enrolled in the study. They were divided into 3 groups according to the culture- or bacterial antigen assay-proven diagnosis and CSF findings: bacterial meningitis (n = 31), aseptic meningitis (n = 65), and non-meningitis (n = 61). Total LDH level and percentages of LDH isoenzymes in the CSF were measured in each patient. Each group showed a distinct LDH isoenzyme distribution pattern, with a statistically significant difference among the groups in the percentages of the various isoenzymes. Compared with the non-meningitis group, total LDH activity in the CSF was high in the aseptic meningitis group (49.82±35.59 U/L, P < 0.001) and exaggerated in the bacterial meningitis group (944.53±112.3 U/L, P < 0.001). Low LDH-2 levels were unique to bacterial meningitis (P < 0.01), whereas high LDH-3 levels were characteristic of aseptic meningitis (P < 0.05). Both groups had low levels of LDH-1 and high levels of LDH-4 and LDH-5. In conclusion, the LDH isoenzyme pattern may be of clinical diagnostic value in meningitis, particularly when culture results are pending.