This study was focused on cerebrospinal fluid (CSF) manifestations in experimental Streptococcus pneumoniae and Escherichia coli meningitis in rabbits. An increased (p less than 0.001) CSF lactate concentration was found in infected animals, mostly not accompanied by a decrease in CSF glucose concentrations. Despite a marked difference in CSF cellular response between the 2 etiological groups no significant difference in CSF lactate levels was found. Neither did CSF lactate levels correlate to CSF polymorphonuclear cell counts. CSF concentrations of albumin were with large variations above control levels in all infected animals. Also a small or moderate increase in CSF albumin levels was generally associated with a marked increase in CSF lactate concentration. The concentration of total amino acids in the CSF was above control values (mean + 2 SD) in 9/21 infected animals. Halothane/N2O anesthesia for 25 min increased (p less than 0.05) CSF levels of glucose, partly independent of alterations in plasma glucose concentrations, in both infected rabbits and in controls.